I like that a lot (although I don't know exactly WHEN to use Substitute), but I'm playing Platinum, I don't have HH or SS, so he can't have Headbutt. Alternative?
Stomp works for the flinch rate.
1. Registeel seems to be good with Iron Head, Thunder Wave, Earthquake and Explosion. Why did you suggest Stealth Rock? What purpose does it serve?
Damages the foe upon switching. Its THE best move in the game, period. https://www.smogon.com/dp/moves/stealth_rock <--click there.
2. How exactly does the Curse Talker Registeel work?
Curse up to get att and def boosts, Rest when weak and nail things with Iron head and Sleep Talk so you can attack whilst asleep.
3. Would having Charge Beam, T-Bolt, T-Wave, and Ice Beam be a bad combination? I would have chosen S-Toss but it can't learn it....Is this set too many Electrical attacks?
Yes, Regice NEEDS Rest and Sleep talk to be effective. Its a special wall and if it cant heal its really rather useless.
4. If you did put together a moveset for Regirock, could you give me at least a few suggestions for what it might be?
I gave you a link in my previous post and explained which one you should use. o_o
Just to clarify, My Regirock has the highest Atk, Regice has the Highest Sp.Atk, and Registeel is equal on both. (So why use Iron Head instead of Flash Cannon?)
For the flinch rate Iron Head has with Thunderwave and so you can beat things its supposed to i.e Mismagius who will just lol at Flash Cannon due to its immense SP.Def.