The dealer tells me that 16" rims won't fit the Verano, as they interfere with the brake calliper and that I must buy the 18" rim/winter combo.
The TPMS has no effect on stability control.
I don't think the recommended tire pressure will change much (if any) between the 16's and 18's. I used 32 PSI in my 16" tires, front and rear.
The car's computer will be programmed for your new wheels TPMS so the original settings are immaterial.
I didn't bother with TPMS for my winter wheels. These are my wheels which came off an older Buick. They look better than the black winter steel wheels and cost less.