I have 100Amp service to my home. I have an electric stove in the
main kitchen whose sticker lists two power ratings: 8.3kW and
10.9kW.

First question: why two ratings for one stove? Perhaps one for the
oven and one for the cook-top? If so, which is the higher?

Second question: I'm trying to figure out if I can add a second
electric stove for the proposed basement kitchen we're considering.
If I've 100Amps service to my house, which voltage (120v x 100Amp =
12kW... or 240v x 100Amp = 24kW) do I use to calculate max power I
have available? Of couse, I'm going to have to consider the electric
load of all other equipment too, but the stove alone is a biggie.

Thanks.
Theodore