Sounds like you've come to the right place, damocles. :]
Your model looks neat

. You do the texturing on that urself?
Good modellers and texturers are always in high demand around here, so if you're willing to get your hands dirty doing some stuff then we'll be happy to have you involved in world building and whateva else might interest ya.
A few more details on the questions you asked..
Theres no particular poly limits (actually it may be 65,000 polys per model - but it can be increased if it was necessary) - but because the model has to be downloaded in the game its often best to try to keep em fairly low-poly if possible. (Also helps to ensure the worlds that use your model are playable for people who have low-spec PCs, like me .. ). That said, if you just wanna be creative and arent particularly bothered about making a world thats practical for live-downloads and low-spec users, theres no particular reason you couldnt go completely OTT :].
The physics setup is controlled via world server settings rather than anything related to the model data - and much of it is jus simple or incomplete at the mo - but you can get control enough to make quite an interesting range of vehicles and objects. (that particular model would look great with control mode 21 methinks :] )
good luck with the finals. Get in touch afterwards and we'll get you access to some of the extra tools download links etc.