If you're clocking up 400 miles a week that going to cost you a bit in an Altezza RS200. If it's all open road driving then a full tank should just last you.
I can't believe I'm going to say this but I think a diesel Mondeo or Golf would be better suited to your needs. Definitely more economical to run but won't be as fun to drive but...
As for parts, most suspension, brake & panel bits are the same so you shouldn't have any hassles sourcing them locally.