Hi, I recently dusted off my copy of FS2 and played it again, after downloading the open source improvements and such. It feels like forever ago that I bought the game at the school book fair

(occassionally they sold computer games).
Anyways I'm a modeler who does work in 3DS Max, and I have a question.
I'm not very well acquainted with game engines, so what can it handle? Say I used higher poly models and better textures with normal maps... could this cause problems with the engine, or would any additional resource use rest squarely on the user's computer?
I ask because I've been inspired to make a mod where you play the Shivans, and I wanted to put more detail into the geometry and textures of fighters and ships (as well as adjusting their scale, changing movement speeds, etc). Generally a faster paced, more realistic mod.