Creeper, sounds like you've got a decent project on your hands. Seeing as you're just getting started, I'd recommend doing a little bit of a cost vs gain analysis on each mod you do.
Shaving weight really helps when you are accelerating/decelerating the car as it lowers the inertia/momentum of the vehicle. Unless you are doing a tremendous amount of stop and go, your return will be poor. The racing seat idea has merit, however from a strictly financial point of view, the break even point is likely not within the expected life span of the car. (I emphasize the strictly financial part of that statement)
Why not start with the cheapies/freebies, like Daox suggested, your best gains will probably be in aero mods. Things such as folding in a mirror on the highway/smaller(aero) mirrors have shown gains as well as the somewhat infamous pizza pan hubcaps or a good 'ol fashioned grille block.
On the note of exhaust modifications, I haven't looked under an optra in about a year, so I can't remember for sure but I think they have a resonator as well as a muffler, eliminating the resonator will give you a little better flow but will make it louder. Making the engine breathe a little easier should give you a little more power without requiring more fuel.
And yes, I'm new here too, but I'm definitely not new to automobiles.
