How do I create low-detail SpaceShip for video game for Ultra-Low End PC?

I already know how to make a spaceship but now I wanna make a space shooter game for Ultra-low spec PC like mine. There will be a lot of spaceship classes and 5 Factions. Spaceships in each faction will be different from each other. So how do I make 3d Model and the texture for those things?

This little thing costing, well, only this much having almost nothing inside can run this 3D stuff.
What is Ultra Low by your definition? Would it be able to control and keep in memory 5 faction fleets while playing?

Make your stuff quads initially and then Triangulate, try to do some shortcuts - delete faces, recreate. Look here for some tricks on modeling/texturing.

I ever played Galaxy On fire 2 HD on a $50 tablet w/ 512MB ram. There was 5 Factions + Some Pirates in one map and the game work fine @ 60FPS