How to compute breaker size for electric Stove + Oven?
I'm not sure about the Viking cooktop. The installation instructions repeat the specs but don't specify a breaker size. It sounds like a 50A should do it, though 48A continuous would actually need a 60A breaker. You may want to check with Viking on that.

The Kitchenaid oven is very clear in the specs:


  Models rated from 7.3 to 9.6 kW at 240 volts (5.5 to 7.2 kW at 208 volts) require a separate 40-amp circuit. Models rated at 7.2 kW and below at 240 volts (5.4 kW and below at 208 volts) require a separate 30-amp circuit.


so a 40A circuit is called for.

You definitely do not want to run those together on one circuit - turn on 3 burners and the oven at the same time and you will overload the circuit.

Both of those on a 100A subpanel is fine, with the key question being: What else is on the subpanel? If it is a few lights, no big deal. But if you have your kitchen countertop circuits (2 @ 20A and easily could pull 15A each at the same time), fan, refrigerator, etc. you might be overloading that at 100A.