Intake and exhaust might net you 1-2 horsepower. Doing a "dual" exhaust on a 3 cylinder wouldn't net anything extra even if it could be done. You could do dual outlets, but that is just more weight gaining no power.
The only way you would gain any significant power is with forced induction, ie turbo or supecharger. There are problems that come with that though. How strong are the internals? How much boost can they handle? How will you handle the extra fuel needs? Being from California how are you going to deal with their strict modding laws?
Even if you went through with all the mods on your list, your car is still going to be pretty slow. Modern economy cars are now putting down 180 hp.
I am not trying to bash on your project, but there are better options out there to mod and hop up.