There are so many options and considerations when choosing a car from scratch, I'll leave that part to someone who's a lot better qualified than I am to pick a winnah, but the "bracket mode" question was of interest to me because I have watched cars pick up anywhere from a tenth to three tenths when switching from "bracket mode" to "killer," which is something they usually only do if they have a heads-up (no breakout) race coming up the next round, such as they'd have when racing a same-class car in the eliminator, or racing in class eliminations.
To pick a car up somewhat, for a heads-up race, from "bracket mode," I have seen racers do thing like cooling their fuel, icing down the intake manifold, running different slicks (ones that hook better, perhaps, or hook as well, but don't slow the car down in high gear as much), drain considerable oil out of the motor (leaving a bare minimum to maintain oil pressure, to reduce crank windage,) getting every last LEGAL pound out of the car for that run, changing tire pressure to reduce rolling reistance and possibly altering total advance to gain the last ounce of horsepower for that all-important e.t. advantage. They could also install taller front tires for more rollout, but usually don't.
I am not a racer (currently) so I am sure I've probably missed a lot of other things that can be done to make a car incrementally quicker in an all-out situation, but these are a few of the more obvious ones I've seen. Maybe a more knowledgeable racer can fill in the things I've missed.
Good luck finding a suitable "class" car... racing is, as you probably know, the most fun you can have with your clothes on... and, I envy you your opportunity to go racing again! Have fun!!!
Bill