Since my post up top, I’ve visited 2 local shops & talked with some really knowledgeable folks about the local karting scene. Your responses were very helpful, as well, and I’ve got a good idea of direction for now.
I got great advice to get a used chassis with the tabs/bracket to convert to shifter; also, a kart with existing front brakes that I can take off for now would be good for future options. I’ll run Rotax Masters or Senior this season, and hopefully move to 80 shifter in the future. I’m leaning toward buying a new Rotax Evo to take advantage (or not) of the warranty.
Rotax Challenge and 80 shifter both are apparently very popular and well supported local classes. A challenge for me is that the Rotax Masters min weight is 405, so that will mean 80 lbs on the kart! Lame. I thought my size & weight would be an advantage so this is pretty disappointing. I can try Senior, at 385 lbs, but then I have fast and reckless teenagers to contend with, according to the local shop owner & series manager.