When I posted I didn't realize you already owned the 70-200 IS and had a budget of 2000-2600 to work with. To be honest you have a vdry strange situation and a budget that is in the middle of a "taop-of-the-line" budget and a prosumer budget so it is very difficult to figure out what to recommend without knowing what you'll be shooting. For example, the 70-200IS is a phenomenal lens on all accounts, however, so is an 600 f/4. Just because you have a phenomenal lens does not mean you need then lens for what you're doing and that is worth it to a) carry around and b) pay for.
First off, and you NEED to answer this question before you can make any wise purchases: Are you more of a telephoto or wide angle person or are these pretty albeit rare shots. The reason why is because you may need to make a choice between a landscape lens and a zoom lens with your budget. and what lenses to go with.
Second, how much are you willing to carry? 3 lenses a body, flash and especially a tripod can be VERY cumbersome. If I'm going somewhere and know that I'm going to be doing telephoto work that has to be extremely accurate I'll bring my tripod but for the most part I like to keep as much home as I can allow myself to. You may think you won't mind carrying it all but it may detract from your experience if you have to worry about all your valuable equipment and lug it around everywhere. Just be careful you know what you're getting yourself into if you carry all this stuff around. You've been warned.
Next, flashes and tripods... I know I mentioned them before but you need to understand that they are an ESSENTIAL part of any kit (especially a pro kit as you are trying to create). Wedding photographers always use a flash and they have the fastest lenses there are.
The benefits of a flash are numerous but the most important are:
1) It allows you to shoot with a better ISO and higher aperture (ie you can actually NOT shoot at f/2.8 if the shot calls for it)
2) Almost always a shot is better with better LIGHTING and NOT better lenses, this is a fact of life - your subjects will look much more natural if you can bounce light off a ceiling for indoors or fill flash for outdoors shots. If you don't know what I'm talking about just take a look at the harsh flash photos of a person in a bar on facebook.
3) Many creative effects are only possible with flash lighting
4) Most basically, the potential for more light is almost always better than less light
If you want to do landscapes you will NEED a tripod because almost all landscapes in the modern era are done at sunset/sunrise (I once read that no publisher will publish anything not done outside of these times it's so competitive now). Because of this need to create a moody picture, you will have very little light at these times and will need a tripod for long exposures. You will also need a tripod if you want to attempt to do exposures indoors without a flash.
OK, sorry for the digressions, but at the level of equipment you're potentially getting you have to know that a flash/tripod are normally thought of as the first add-ons to a walk-around lens and body and will make more shots available to you than will faster glass.
Now, if you sell your 70-200 for $1500 (not unreasonable at all)your budget is 3500-4100 to get an ultimate kit.
First off, you don't NEED a 7D, a 550D or 500D will do you fine (and the one I would recommend) and a 50D would be fine as well if you want the extra build quality but since it can't do video I would not recommend that as that was listed by you as an important feature which I think is fair. The reason being both can do video, and you are not using the most important aspects of the 7D which are increased frame rate and better AI servo technology. The 7D is really a specialty camera mostly for wildlife photographers in my opinion but for regular shots like you will be doing a 550D/500D will be MORE than enough.
Having said that, bodies are upgraded all the time and will always have new features so it's not a huge deal to upgrade. However, if you are sure you're into this and want to go a level up I would skip the 7D and go straight for a 5D M2 (for the video) as a 5d M1 doesn't have this option. Full frame is quite a difference and will change your lens choices drastically and REQUIRES you have buy an external flash for a 5D...
So first question is 550D/500D or 5D M2 which is a difference of $500 for a used 500D to $2400 for a new 5DM2 so obviously this is a big choice.
Personally, if there's one thing I wouldn't get used it's the body. A few reasons being that it has moving parts so the life of it can really be judged by how its been handled by the previous owner, two, you will not really be able to tell the sensor quality without doing a large blow up shot analysis and by then you will already have bought it and three, people lie about what they are selling. I'm going to actually assume you buy the body new because that's the only way I would do it and if you're going to get the lenses used that makes more sense to me.
After all that here are the recs:
Middle of the line kit that will get the job done VERY well and not break the bank:
550D + 17-55IS (this is MAYBE the ONE lens that can get away without flash as it is f/2.8 IS).... but I would still recommend you add on a flash
flash
add on flash if not too much to carry around
add on 10-22 + tripod if considering wide angle shots
keep 70-200 if considering portraits and more zoomed shots
add on 55-250 if only occasional telephoto shots
Pros: Cheap and will definitely make amazing shots (this is the same lens quality as a 24-70 on a 7D sensor = quality that will be very difficult to differentiate from the higher end options), very light walk around combo if you choose to use these together, and ability to use 17-55IS (maybe the most versatile lens in existence), do not NEED to buy a flash because it already has one
Cons: Not full frame, 550D with lower build quality
For $900 for body and $900 for used lens = $1800 you would be below your $2000 budget and could keep your 70-200 and even add on a flash. If you sold the 70-200 you could get a 10-22 + 70-200 non IS f/4 or possibly if luck a 70-200 IS f/4 which would be a very fine setup indeed. Also, just to put it out there like the previous poster did, a 100-400 is a very nice walk around lens that is HIGHLY versatile and takes great shots (and can be handheld if you're careful - I speak with personal experience).
Top of the line kit:
5D Mark II
24-105 or 24-70 (I'll let you choose)
430 ex II flash
add on either 3rd party or wide angle or 16-35 + tripod if you need wide angle
add on 70-200 f/4 (IS or non-IS depending on price) or 100-400 if you need telephoto
This comes to 2400 for new body +700-1000 for lens + 300 for flash = 3400-3700 which would require you to sell the 70-200 (which I recommend anyway). The last of the money you would have to make a choice between telephoto or wide angle unfortunately with your budget as there really are no cheap canon made wide angle options for full frame cameras.
I could obviously go on but this post is too long already so have fun making these tough choices and let us know what you choose.
