To be honest I disagree on the 30fps smooth issue; I have my fps capped at 30fps by Oblivion Stutter Remover (something else you should look into because it has features that bring major fps improvements as well as removing stutter i.e. making things more smooth, even if you're not interested in capping frame rates). But different people have different standards, so y'know, each to his own (on fps).
Looking at you're list however, you're not going to be getting 40-50 fps anywhere other than a few wilderness areas. If you went for a light install of REAVWD (you're 2) and install an extra low spawn rate plug in for FCOM (which, btw, will still be a higher spawn rate than vanilla), you should be in the 20-30fps zone in most areas (a few city areas may be somewhat lower, but above 15fps, which is the threshold for city areas to me).
The problem btw is going to be the NPC's, particularly with FCOM and 6) running together. What happens when when two travellers from Crowded Roads bump into two bandits from FCOM before a merchant and her guard join the fight from Tamriel Travelers and then two guards from OOO join the fray to take the bandits out. See, slowdown. (now imagine with the default spawn rate of FCOM and its five bandits rather than two

bliviongate: :brokencomputer: )
On things you're willing to give up
1) You'll get good performance improvement and probably won't notice anything much different graphically
2) I have never noticed a single fps change regardless of what I put my grass settings to, even without low poly grass, but hey, installing it won't do any harm so...
3) Pretty much essential, since you'll get a CPU bottleneck before anything else.
I have been reading up on PFFIYing meshes (from the 50+ steps to no CTD thread) and will be doing that. It will be a long setup but I know it will be worth it. Are my goals reasonable to have a smooth framerate of 40-50FPS? 30FPS is playable, but still not that smooth - and I know if it is 30FPS then when it comes to heavy combat it will drop significantly - my dream is to be able to be in big battles with mages summoning and spells flying and not have a CTD or slowdown (something I couldn't do last time I played).
PyFFing meshes will make a huge difference; that's the right mindset to have going there. However, no, I don't think you're going to be able to have 40-50fps and game that is as well modded and good looking as you are planning on. Also, big combat scenes are simply impossible in Oblivion; it doesn't matter if you have 30fps or 50fps to start with; a large fight scene will bring your computer to its knees regardless (engine and AI problems on the inside).
I don't want to sound like I'm being discouraging, but its just that performance vs mods/graphics in Oblivion is a hard bullet to bite and I've had to make compromises and ultimately you probably will too. But the best advice is to give it a try and see how it turns out; if anything else it will bring you closer to your goal.