i have the same car. the auto won't give you any disadvantages as far as modifications, but the performance mods won't seem to enhance as nicely as if it were a manual tranny. you can buy and install anything that a manual would, save for clutches and short shifters.
is any of that understandable?
oh yeah.....i suggest you wander over to www.sr20deforum.com
it has more extensive info for the sr20 owner.