Welcome!
Expect high 13s in stock form. The winning stock Ty at nats ran a best 14.01 (hot and humid). Note that some of the numbers given above are at higher than stock boost levels (will and sy2206), so don't freak out if you can't do 13.5 with 15 psi.
Any premium 6X9 will work in the rear, but you may need a aftermarket grille that extends out an inch to provide clearance for bigger magnets. I'm running some Infinity's that fit (barely) with the stock grilles.
The fronts are problematic. Most premium 4X6 will have clearance problems at the magnet, especially on the driver side. I'm running some Polks that sound good, but I had to hack the grilles and file the back corner of the instrument pod to get them in. Plate units (infinity, etc.) will fit better, but I didn't like the sound nearly as much as the Polks.
I've owned 3 S-blazers/2Tys and found the bass to be lacking with every stereo config I tried unless I added a subwoofer of some sort. Don't need a huge thumper, but something. I currently have an amp and 6" pioneer free-air unit embedded in the tailgate. Doesn't get in the way, but fills in the bottom end. HTH, and once again, welcome.