Apologies about the long post, just trying to sort out where I should be looking.
Lots of questions, so lots of answers coming. At the end of the day, you have to answer these questions for yourself, but some good advice helps...
I'm working on the 'assumption' that getting lenses that suit sporting events will be suitable for most distance wildlife photography.
Maybe true, but it depends on the sport. You mention bike rides and triathalons - generally, spectators and casual photographers at those events can get pretty close to the action - close enough that 200mm is likely plenty of focal length. That might not work for wildlife, possibly for big game on a safari (where you sometimes need a wide angle for wildlife - in Ngorongoro Crater, lions and elephants came within 5 feet of the Land Rover we were riding in), but not for small animals/birds, where even a 400mm lens comes up short. If birds/wildlife is an occasional thing for you, a teleconverter makes sense (more on that below).
I just ordered a EF-S 10-22mm, a 70-200mm F/2.8L IS II, and a Tiffen 77mm UV/CP/ND kit with it, they arrive in six days. Excited.
Great choices! The 70-200mm II is a great lens, and I really liked the 10-22mm angle of view (I had one, which I sold when I added a 5DII and 16-35mm f/2.8L
II to my kit, giving the same angle of view as 10-22mm on APS-C).
I disagree with the blanket statement that EF-S lenses lose value quickly. Some do - kit lenses and lower end lenses in particular. But three current EF-S lenses deliver optical quality equivalent to many L lenses (when used on APS-C), and hold their value well - the EF-S 10-22mm f/3.5-4.5, EF-S 17-55mm f/2.8 IS, and EF-S 15-85mm f/3.5-5.6 IS. FWIW, after using the 10-22mm for about a year, I sold it for only US$50 less than I bought it for (new from Amazon.com), and that was before the recent spate of lens price increases - selling it today, I likely would have made a profit.
I am considering the EF1.4x III Teleconverter. I'm worried about the weight that the 70-200mm F/2.8 IS II is going to add to my bag and my tiny camera already, so the Teleconverter is looking rather special at the moment compared to a 100-400mm L.
For occasional use, a TC is fine. Personally, I would not plan on it for frequent use. More later...
Another option would be a mid range say, 24-70mm to replace my 18-55mm kit. I would pair either with additional filters (gradient NDs, an expensive IR - though supposedly the 450D produces really terrible pseudo-IR photos) and maybe a new tripod.
With the 10-22mm in your kit, a 24-xx L zoom would work. You could also look at the 24-105mm f/4L IS - on a crop body, it's a useful focal length for outdoor shooting.
I'd skip the IR filter - dSLRs aren't really sensitive to IR, because the Bayer mask (RGB array) covering the sensor blocks almost all light outside the visible range. There are 3rd party vendors which remove that mask (IR conversion), which would be the way to go if you want to shoot IR on your 450D (after getting a new body, that is, unless you only want to shoot in black and white going forward).
I'd like to keep my focus mainly on zoom lenses - I understand the desirability for primes, but the sports shots I work with often don't let me work around that, and lugging around something like a very expensive 400mm prime when I only have one camera is rather tricky.
Zoom lenses are for convenience and flexibility. For example, you just got a 70-200/2.8, but the 200mm f/2.8L II prime lens gives you the same long end and aperture in a package that's 1/3 shorter and half the weight.
IMO, the main reason to get primes is for the faster aperture - the fastest zooms are f/2.8, but if you need to stop action in low light, f/2.8 makes that challenging. Similarly, if you want to stop action in low light at long distances, those heavy supertele primes (300/2.8, 400/2.8 ) are often used by pro shooters, but with cameras that have better ISO performance than your 450D.
However, I was told that it is more beneficial to get a cheaper secondary camera (like a duplicate 450D) or to save and get a 5D Mark III than to look at the above options. My questions stem from the following:
Depends on the benefit you want to achieve. For a working photographer shooting events, a second camera is almost a must-have. Are you getting paid for your shooting (you mention charity events, so possibly not)? Cameras fail, and if you're getting paid for covering an event/wedding/etc., 'sorry, my camera broke' doesn't cut it for the client. But if you're just a casual shooter, carrying a second dSLR as a backup is not really necessary, IMO (if you're concerned, bring a P&S).
The one exception to that might be if you're using prime lenses, so you can hang both cameras off yourself and change focal lengths quickly. But that's why you're using zooms...
At what point does having a better camera outweigh getting better lenses? I'm not finding that I'm missing shots or anything with a slower fps, nor do I mind the lower pixel resolution as they all get reduced to a a max 1200x800 jpeg size for distribution. I see the benefit in the 7D with the additional AF points and the ability to use my EF-S 10-22mm, but I don't see the draw of a 5D Mark III yet.
At the point where you feel your camera is limiting your shots (or when you own all the lenses you could ever need/want). Personally, I started with a 500D/T1i, and I did find it limiting. Compared to your camera, the 7D's autofocus system is a dramatic improvement. Compared to your camera, the ISO performance of a 5DII is a dramatic improvement - the 450D tops out at ISO 1600, and you might not even find that useable, whereas the 5DII produces useable
images at ISO 3200.
Another limiting feature is AF microadjustment - as you get faster lenses, you might find they are a little off with a thin depth of field. AFMA can correct that (so can a trip to Canon for service, but you need to send in your body and all your lenses). With fast primes, I'll never get a body withour AFMA (my 100mm f/2.8L
Macro IS was backfocusing on my 500D, for example, but I worked around that because I shoot mostly manual focus for macro work).
What should I be considering as my primary goal in achieving a light and daily general use bag of equipment? I am thinking I need to keep my 18-55mm and my 100mm Macro for my standard everyday bag. I should be able to use my camera's inbuilt flash for anything tricky. I think this limits the versatility of what I have, but will give me a light and small bag I can actually walk around with without falling over.
That's always a trade off. On a recent trip to China, my photo gear bag weighed in at about 10 kg (all packed in a LowePro Flipside 400AW, which was in turn packed into a Pelican Storm im2500 hard case for a 15 kg total carry-on).
I suspect if you get a decent general purpose zoom (24-70, 24-105), you'll carry that instead of the 18-55mm kit lens - you might need a bigger bag.
It has been suggested that the 50mm and a 70-200mm would be better, but I'd consider buying another lighter lens that wouldn't weigh 3.28 lbs or 1.5 kilo for daily use, if this is the case, what would be recommended?
The combination of a general purpose zoom and a 70-200mm telezoom would cover most needs. I do disagree with the previous poster stating 24-70 + 70-200 - that would be fine on a FF camera, but on a crop body, 24mm is not even wide angle (38mm FF equivalent). However, an EF-S 17-55mm f/2.8 IS with the EF 70-200mm f/2.8L IS II would cover almost all your shooting needs in a 2-lens kit.
If I chose to go the route of a teleconverter, what primary issues will I be dealing with in relation to using it with a 450D APS-C sensor? How difficult is it to remove quickly and replace the 70-200 on a camera? I know that it will reduce the aperture, but it was the reason I chose the F/2.8 instead of the F/4.0. Is the clarity on the 70-200 worth the teleconverter over getting a 100-400L or a 70-300L to fill in the gaps? Is it possible/actually worth considering using the 1.4x on any of the other lenses I have? I've only seen reviews of it paired with the 70-200mm. I looked at the benefits of the 2.0x and the 1.4x teleconverters, and I've seen the suggestions that the 1.4 is better with regards the quality. Is this still the general consensus?
First off, of all the lenses you've mentioned, the only one a Canon TC will work with is the 70-200mm zoom (they are compatible with 135mm and longer L-series primes, the 70-200mm L-series zooms, the 100-400mm but you sacrifice AF unless you have a 1-series, and a few miscellaneous lenses like the TS-E series). You could get a 3rd party TC that would work with other lenses, but IQ is not as good.
Yes, the 1.4x III causes less of an IQ hit than the 2x III.
I really recommend using a TC for only occasional use. For routine use, buy the focal length you need. A possible exception would be the supertele primes - a lens like the 300mm f/2.8L IS takes only a very small IQ hit even from a 2x TC. The 70-200 II holds up pretty well to a 1.4x, and decently to a 2x. There's a whole other thread
on the latter, and I also posted a shot with the combo
on my 7D. I also have the 100-400mm, and the IQ is definitely better with that - not a lot better, but noticeably better. I got the 2x II for use with my 70-200 II as a weather-sealed alternative to the 100-400mm.
Swapping on and off a TC is a hassle, especially in the field. You'll likely miss shots if you need to do that frequently. For situations where you need to go from short to long quickly, consider the 70-300mm L or the 100-400mm - either would be a lot more convenient than 70-200mm Â± TC, and deliver better IQ.
Yes, you'll lose effective aperture as you know, but that's not the only downside. Less commonly known, but possibly significant, is that AF is slower with a TC - by design, when you put on a 2x TC the camera will slow down the AF by 50% (25% for a 1.4x TC). That might be an issue for fast moving sports (you would notice it compared to the 70-200 II without a TC, yes, but compared to a non-USM lens like the 55-250mm you've been using, even 50% slower on the 70-200 will still be faster than that).
Hope some of those answers help. Good luck with your decision!