As far as which muzzleloaders are legal? I believe what ever muzzleloader was legal before Idaho Fish and Game changed the rules and then switched back, are now legal again. The only rules that have changed are, no sabots, loose black powder or it's substitue only, and the projectile must be all lead and sized to within .01" of the barrel diameter, I think?
If you went with a traditional, like a Lyman Great Plains Hunter, you would really not be at any disadvantage in my opinion. I think they are more fun any way! I believe the thompson black diamond would also be legal again.