Thank you so so much.
1. Do I need another monitor besides the LCD on the camera to check focus etc?
Not 100% necessary, but useful. The more you focus pull the more necessary one will be.
You can view at upto 10x for the initial focus. Eyepiece LCD viewfinders such as Zacuto are available as well
2. Which is the best slider for price for DSLR?
sorry not my area - try Planet5D or similar websites
3. Which is the best way to record audio? Do I record on camera or external recorder and sync using a slate? I have a BeachTek DXA-SLR available for free. Is it any good?
External recorder - you can sync then using a slate or software such as pluraleyze. can't comment on the Beachtek
4. Should I use Magic Lantern software or original Canon RAW? If magic lantern, then which version?
Canopn does not record RAW Video. Regardless of whether you record RAW or not the Magic Lantern is recommended for the 5D3 (not available for the 1DX) for focus peaking etc.
5. What is the ideal ISO for video? And if not ideal, what is the acceptable range for noise free work.
ISO160 or multiples thereof if required
6. Is 1/50 the only shutter speed to work at or it does not matter?
You can set the Framerate in the camera - so depending on your output you would set the shutter speed at double that.
7. Will my Imac be ok for the edit? I will not buy an Imac now until it is refreshed, but just want to prepare myself on the speed of edit.
Can't answer that - but I suspect it would be a little slow for RAW Video editing
Further - one Card ?? You will need several - or a stack of them if recording RAW Video....
ANY help is appreciated sincerely.
This takes me to few other questions:
Which monitor should I buy which can stick on top of camera?
Which version of Magic Lantern? (I believe the latest is in testing)
I do not understand "set the frame rate in camera"
Yes, I need multiple cards. If I was working 12 hour days and recording 5-6 hours of RAW video, how many 32 GB cards does that translate into?
One thing to note is that the Magic Lantern RAW recording is currently unstable
and not even available as a pre-built alpha. At the moment they highly recommend not
using it for anything important. It's also only available on the 5d3, not the 1DX, so make sure you take 1 or 2 backup cameras just in case. You'll also only get ~6 minutes per 32GB from what I hear, so you'll need a huge stack of them, and lots of external HDD to make 2 copies after each day. If you shoot 6 hours of video per day, you'll be over 2TB of total space which is 68 32GB cards. Due to not filling up the entire card, you'll probably need 75-80 cards to be safe. Then you need to download each and ever card to 2 separate HDD, which means you'll be burning using 2 3TB drives a day (although you can use the extra space left over for the next day).
I know you said need professional results as opposed to lighter weight, but why not go with the Canon C500 which offers a RAW output mode. I think you need an external recorder to record in RAW, but it'll be with fully supported workflows, and it's not a huge camera from what I understand, only slightly larger than the 1D style body. Plus you can have your EF lenses as well on it.
For any field needs, your iMac will likely struggle for any RAW files, even the fully supported C500 RAW files. Even if you max out the RAM, the CPU is going to be fairly old, especially compared to the new Intel CPUs that are just about released. If you insist, you might want to look at a small PC with a top end CPU and decent graphics OpenCL/CUDA card with gobs of RAM that you can use to convert the RAW footage to ProRes or whatever you're preferred editing format is. And don't forget your backup requirements for that, which will be just as substantial as the RAW footage.
So all in all, you'll need a car-load of hard drives to cart around all of your RAW footage, a small cluster of fast (but can be small) machines to convert all that to a format that can be edited. And then you actually need to edit all that footage, which you'll ideally need something quite a bit newer than your current iMac.
Or...you can use the 1DC/C100/C300/C500 with their higher quality 1080p compressed output which will save yourself a ton of hassle, save a ton of space for required backups, and still have great quality for your needs. You probably should still have a better machine, but the one you have is more likely to manage OK.