The Commissar Lord doesn't have Stealth, he has +1 to his cover save, which he does not pass on to his unit.
Meltaguns are better than melta bombs. I take enough casualties from my own vehicles exploding, piling my guys around one and then intentionally blowing it up to lose a sixth of the squad is just bad news. Meltaguns also help kill heavy things like Plague Marines and monstrous creatures.
I think Rough Riders are poor. I've tried very hard to make them work, but even with furious charge, two attacks at WS3 just doesn't do enough damage. And they are useless after that one charge.