First off, I'd narrow down your field of view to say two cameras. And then decide between them. For example- out of the 7D/60D/T4i mentioned- I would go with the 7D/T4i - because, in a lot of ways- the t4i can do almost everything and has most of the features - minus larger size and ergonomics /controls of the 60D- kind of a mini-60D+. It makes up for some of the controls of the 60D- with its useful touchscreen- which works well.
I see it often enough here on POTN. Guy buys a 7D or other more pro camera- and then finds out that it's too much.. Reality is that you could easily start on a 7D and it'd be fine.. Disappointments: Off the back- the sophisticated AF system is a bit much for most- but if you bite it off a bit at a time- it's doable. You've been exposed to DSLRs- so you really should not have that hard of a time.
Video: As long as you are aware that video on a 7D is basically a manual autofocus /manual focus operation- great. The 60D is similar in this respect- except for the swivel screen on it makes composition easier. It's not a camcorder- with true automatic autofocus.. If you are looking for that- you should consider the T4i instead- with the 18-135 IS STM lens. Still, overall, you might be better off with a dedicated camcorder.
As far as shooting sports and other things that a 7D is designed for- well- most are just as well served by even lesser cameras. Even older Canon DSLR's should be able to fill these roles- although newer models will serve them possibly better or easier. For most- any current Rebel is sufficient for the task. For what most consider sports- taking pics of young Billy swinging a bat at Little League- you really don't need a 7D to handle that- it's probably overkill. LIke the 60D, the T4i sports a 9 point all cross type AF system- so very similar.. Having all cross type af points helps shooting in AI servo - for sports..
Growth: The 7D will provide you a lot of room for growth- that I won't argue. But in the end- it's just a camera- just like the Rebels. The 6D/70D will give you a brighter viewfinder and a bigger body and more controls- T4i is going to be more likable by those wanting a smaller body, like women, or those just plain tired of holding up a hefty DSLR. A T4i makes up for having fewer controls- with that fantastic touch screen.. Either one will last you a while- neither will hold you back- deep down inside- they are both cameras with similar underlying architectures.
Personally, I'd look at what features you really want, and the size of the package that you want. I'd suggest trying both and seeing what feels better in your hands- and what you will be comfortable with in the long haul. A T4i/60D has that swivel screen that is amazingly useful for certain types of photography.. The 7D- is the feel that it gives in the hand- it feels substantial.. That said, it feels better with more substantial lenses on it.. This is where bigger bodies work wonders- when you start putting better, which means usually heavier, glass attached to them. IF I had to narrow down the field to two cameras for you- I'd pick what I have for my crops- the T4i and the 7D. For video, and a lightweight camera - I thought the T4i with the new kit lens would excel - and it's really a wonderful combo. When it comes to mounting heavier lenses- for other things- 7D. On one hand- you have the t4i- top of the Rebel dogpile. And then you have the 7D- King of the crops. At least- Canon crops..
Flashes- go with a 430 EX II or a 580 EX II.. Until you put one on your camera ( or use it off camera ) you won't understand how much it truly adds.. The only way to beat having one 430 EX II/ 580 EX II- is to go with two of them! It's a different ballgame after that.
EOS 5D III, EOS 7D,EOS Rebel T4i, Canon 70-200 f/2.8 IS II, Canon 24-105L, Canon 18-135 IS STM, 1.4x TC III, 2.0x TC III, Σ 50mm f/1.4, Σ 17-50 OS, Σ 70-200 OS, Σ 50-500 OS, Σ 1.4x TC, Σ 2.0x TC, 580EXII(3), Canon SX-40, Canon S100
Fond memories: Rebel T1i, Canon 18-55 IS, Canon 55-250 IS, 18-135 IS (Given to a good home)...