To answer your questions:
1. There's some online vendors that sell gimmicky aftermarket parks such as extended mag releases and such, but aside from t97.ca we're kinda SOL as far as aftermarket or even replacement parts go. Personally I don't think those aftermarket parts are really worth it.
2. The Gen 2 T97 (which is what I have), aside from the stock flat top rail, which is pretty nice and low profile, has an ambi mag catch, and a modified feed ramp to prevent severe FTF malfunctions (ones which push the bullet back into the case lol), however in my experience there can still be FTF malfunctions depending on what type of magazine you are using, usually on the first round. IMO the the only good mod I'd get on the T97 Gen 2 is the LHG, but t97.ca is out of stock on it, with no restock time listed, which blows big time. Personally I'd go with the G2 over a G1 with the t97.ca FTU.
3. My Gen 2 T97 really likes E-lander steel AR magazines, both 5/30 and 10 round pistol mags. Otherwise the stock Norinco mag it comes with works great, but beware of polymer magazines and C-Products LAR mags... those require modification in order to insert into the mag well. Also for some magazines you can push them 'too far in' when loading with the bolt held open and cause a FTF on the first round. You just have to be careful and seat the magazine properly by pulling it back slightly after the mag catches when loading on an open chamber
4. The safety is pretty awkward to use, so if you're used to an AR style safety it is definitely going to feel weird and be slower to turn on and off.
General comments:
Ergonomics takes some getting used to but once you've got it, it's a good compact rifle for target shooting, run and gun drills and LARPing. It is reasonably accurate (2-3MOA) out to 400 yards or so if you decide to mount a scope, and prefers heavier .223/5.56 bullet types such 62gr M855 or Hornady 75gr BTHP due to the 1 in 7in twist. As far as reliability goes the only malfunctions I have had were due to magazine issues, otherwise I do some very basic cleaning after every shooting session and the action cycles fine. If you decide to buy a G2 the first thing I would do is to remove the flat top rail screws and apply locktite to prevent the them from walking out after a few hundred rounds.