SKUSA is a West Coast based operation. If you want national competition here, you run USPKS which is a great series. Besides, the TaG competition level is just as good if not a bit stronger than the shifter level anyway. Plus, you can run SKUSA or USPKS if you have a TaG engine, not to mention almost every other legitimate series as well. TaG is pretty universal around the country.
Local support of a chassis brand is more important than the actual kart itself. Almost any chassis can win with a competent driver/tuner.
At a club level, a 6 year old kart is probably fine. Just make sure it’s in good shape and the frame rails haven’t been flattened. Birel (now BirelART) and Energy are both good brands. Not sure if anyone is working with Energy karts these days though.