A center column always adds instability. I'm sure the RRS one is sturdy, and maybe ok for a light load, but not with something moderately heavy.
Leveling base? Are you planning on using a pano head or gimbal head? If so, the leveling base is great. If you're using a ballhead, it's not really necessary, IMO. The handle on the bottom is how you loosen the base to adjust the tilt, then lock it back down. As for the hook, the tripod ships with a simple platform installed, and that platform has a hook. You remove the platform to install the leveling base, and the hook can be unscrewed. I believe the leveling base has a little cap on the bottom of the handle that can be popped off, and the hook screwed on instead (I actually got the longer handle version for more leverage when leveling with the 600 II on the gimbal, and I got the one with the hook preinstalled). I'd call RRS and ask, but I suspect you don't need to buy the extra hook. (Of course, they sell them - people lose things! They also sell the rubber ball feet even though they come with the tripod.)
Ragarding the plates for camera and lens, not sure why that puts you off. They aren't required - you can get a ballhead with just a platform, it's cheaper and has a 1/4"-20 stud that you can simply screw your camera body or lens foot onto. But do you really want to do that every time? You're paying for the convenience of a quick release system. The nice thing is that RRS uses Arca-Swiss type plates, and most of those systems are interchangeable (not Novoflex and a few others, there are compatibility charts out there). What that means is you can use a mix of plates and clamps from several vendors. Personally, I have both Wimberley and RRS plates, and I have Wimberley, Kirk, and RRS clamps, and they all work great together.
As for cost of the plates, the RRS plate for a 70-200/2.8 is $55, and the Wimberley P-20 (which is what I have on my 70-200/2.8L IS II) is only $3 cheaper. The RRS plate has a 1/4"-20 threaded hole, should you want to attach something else (monopod without a clamp, for example), whereas the Wimberley plate does not (I ordered the Wimberley mainly because B&H sells them, so I get them overnight with UPS ground, whereas RRS takes several days to get to me). The RRS camera plates are also not significantly more expensive than something like a Wimberley P-5 (again, <$10 more); the difference there is the Wimberley is a universal plate that mounts on any camera, while the RRS plates are specific for a particular camera (and there are different ones for gripped vs. non-gripped). The advantage to the RRS plates is that they have a custom lip that wraps around the edge of the camera, meaning no chance the plate will twist when in use (and that can happen with the Wimberley). L-brackets are obviously more expensive, but again, you're paying for convenience - being able to balance a load upright for a portrait shot, vs. using the drop notch, being able to take portrait-oriented panos, etc.
I guess the bottom line is that you pay for quality and convenience, and RRS delivers.