make sure you get an OEM cat... Magnaflow makes one, but the most important thing to building your 2nd gen CA correct is to make sure you are using all CARB legal parts on the intake and exhaust. look for parts saying they are CARB pending or exempt or say "50 State Legal". With your exhaust be sure you don't get an exhaust that is not track rated... street legal exhaust should be under 93Decibels... otherwise you could get pulled over and cited.
Tanabe makes a great exhaust system for the DA that is very nice if you like the OEM style look.. Some people seem to like the cheaper ebay exhaust kits. Alot of what you do is depending on your budget & `how much pride you take in a build...
Drawback to modding the heck out of our cars especially in CA is the high rate of theft.. Our DA's are relatively easy to break into. hence why a clutch lock, CLub, quick release steering wheel, kill switch, working alarm are all good investments to factor in while doing your build.
you won't be disappointed in that DC header. the one you will want is the 4-2-1 Ceramic street header part number AHC-6003
Having an RS you aren't limited to the strut bars you use up front as that model doesn't have ABS in the damn way like my GS does LOL, so you can go ebay cheapies or bling out with a cusco, neuspeed, skunk 2, RSR, Password JDM or any of them you can find... Strut bars will not have a noticeable effect for daily street driving, but are helpful if you live by the mountains, or plan on tracking your ride later on. you may want to look at aftermarket suspension too. again the sky is the limit there and there are a ton of available shock spring combos... too many to list.
You basically have one of the most highly modifyable cars in history being an integra owner... the sky is the limit, look around, google your brains out for anything 90-93 integra related... I could write an entire website and not cover everything there is out there for our cars.
