Actually since I am just a converter and concern myself with modding, the first question I never explored... From my POV many people play it (it's a classic space shooter favorite and blamed by many for the downfall of Wing Commander - It wasn't, please blame Origin!)
Aside from it's existing fanbase (since the late 90's) massive exposure from Spacebattles.com and more widely Sci-fi.com itself around 2 years ago created a huge
influx of people new to the game (For the BSG BTRL mod, you no doubt noticed it on this site).
This site hosts around 15 other MODS but the majority of users are new people now and think it's a BSG site!!!!!
Anyway to show you how influential this game is in the genre, Derek Smart (he who should NOT
be named) once stated he was going to try to buy the FS2 license from Interplay. In the end he didn't (thank the Universe!)...
Since then our little community keeps growing and there are several sites dedicated to FS2. This site is the "little Sister" site of HLP or Hard Light Productions. HLP and Sectorgame/FS2sector are the two MAJOR sites that survived since the days that Volition (the game makers) stopped forums and active support for the game.
New players continually discover (or re-discover) the game thanks to the Source Code Project and the buzz that is generated in Magazines and demo disks (usually in Europe).
The SCP took a decent game and made it almost comparable to retail games you can buy NOW. Of course there is only so much you can do with a 10+ year old game, but SCP has extended the life of FS2 indefinitely until someone else takes a serious stab at the Space Shooter genre...
Starshatter is the only serious contender I can think of off the top of my head.
However FS2 was intended to be mod friendly and continues to be easy enough for complete noobs (like me), can actually see some of their ideas materialize in game.
If someone told me in 2001 I was going to be head of a Robotech project (and Star Trek) and have not only SDF-1, but VF's in a space shooter and do voice acting, and have the illusion of planetary surfaces/atmosphere I would have called them a complete LOON!
As for the models, we have them from many sources (they are credited in one of the main stickies). Models come from many formats, as long as I can use 3dexploration to convert them to .cobs (the necessary evil of FS2, as the max importer is still "buggy" according to our max experts). Or better yet if model makers can save/convert to .cob (Calligari Truespace format) themselves to keep errors to a minimum!
We've had models made from many major formats like C4d, Rhino, LWo, MAX, Blender, ect... Doesn't matter what program was used, long as the end result is .cob they shouldl work. SCP is developing bump maps and normal maps with varied success, added glow and shine maps thus making the old resources come more alive!
As for poly limit, we really don't know what the hard limit is now. In retail the limit for decent performance was around 2k max for a fighter and 6k for a super cap ship.
Now I convert 8k fighters with no performance problems and our largest capship ever ported to game is 60k-69k-ish WIP PEGASUS for BSG:BTRL!
The only other limitation I can think of for models if a hierarchy thing. Models should be one object, optimized and clean with no duplicate polygons/verts, points under 20, and IF they do have subobjects (usually visible systems for destruction or things like turrets) they should be under 850 polygons. (I am NOT a modeler so I don't even know what I just said, lol, you just memorize that dogma I guess.)
Models can now be animated and have moving parts, but please don't ask me about that!
That's the basics. But for expert advice I recommend you take this to the general forum here on Game Warden or over at the HLP modding forum:http://www.hard-light.net/forums/index.php/board,8.0.html
I am biased cause I love this game, but am not the very best source of information about it's true capabilities/limits.