You probably won't need any avalanche gear or preparedness. Most kite terrain doesn't really merit that...but if you snowmobile through some areas & conditions are right some trails can take you through runout zones....but ... it sounds like you won't be doing that. The only reason I suggested watching various avalanche forecasts is that they will discuss daily changes in snow types & quality - there's many variations that could make one area preferable to others.
I wouldn't worry about the 14M. 12M, 9M, maybe a 7 should have you guys in good shape. 14 would only be necessary if the powder is way deep & winds are lightish.
The Bighorns are amazing & Billings is typically almost as cheap to fly in & out of as SLC. But .... there's not much good ski area options nearby. Red Lodge is typically crappy - especially early season. Occasionally they get a huge dump but don't expect it. Its possible that all of the places you're considering will be in great shape by early Dec....but best to watch patiently before plunking your $ down.
4WD rig? You may not need 1 but then you might Really need one - especially if you're not used to driving in snow.