I'm not sure what the T1 and T2 classes are but here are some good mods to start with that will allow you to stay in stock classification in a SCCA solo2 autocross.
#1 mod. Change the shocks. Stock shocks are crap, they give you no stable feel for the car which is essential in autocrossing. Any aftermarket shocks are legal as long as they use stock mounting points. Bilstein HDs dampen the stock springs very well. If you may possibly get springs down the road, you can't go wrong with koni single adjustable sport shocks.
Front swaybar can be changed. Rear cannot. A good setup for this would be a 32mm aftermarket front bar with the 19mm stock rear. 35mm is actually best but more suited paired with a rear 21mm aftermarket bar.
any brake pads can be used
stock rim and stock tire sizes must be used. This means you can use other rims with the same offset size and width with any other tires with the same height sidewall and width (given they are DOT legal). Note some clubs provide street tire classes which is recommended for new drivers. In that case a scca street tire legal is 140 treadwear or higher.
any aftermarket catback exhaust can be used behind the stock ypipe
Mods that will bump you into street prepared classes:
rear swaybar, intake lid, headers, clutch changes, gears, aftermarket hoods, wings, etc
Mods that will bump you into street modified classes:
welded on subframe connectors, forced induction, heads, cam, intake manifold, car body sideskirts, control arms
Please correct me if I am wrong on any of these things as changes get made all the time to the rules, and I also may just be plain wrong
. In any case hope this helps.