Re-Painting

I'd agree with Red here, prep is everything and yeah you miss out on so much of the learning if you don't dismantle. Of course on the other hand, there's a higher risk of messing up the whole thing but once you've dismantled a few you'll soon get to learn their anatomy and you'll be cracking them like nuts in no time.

I will humbly disagree. Not to step on any toes but if you don't take him apart, you will not only skip the learning process but you will end up with paint rub. You can't get inside a joint without hours of light sanding. Some people do paint without breaking it down but the end result is usually obvious after posing. Just my opinion and preference though.

Yeah, don't bother taking him apart them. Not worth the extra effort.

He will just be strait Iron man.

Are you just doing a straight Iron Man repaint, or are you turning him into a different character? If he's staying an Iron Man, I honestly wouldn't bother taking it apart. If you are turning him into a War Machine or something like that, then it might be worth the time to disassemble him.

yea this is my first one, its a marvel legends iron man.

Honestly I've heard of people taking it apart, and people leaving them together. I'll leave the figure together and prep the joints with a dremel and an x-acto to prevent paint rub. Then I'll usually paint the joints first, that way any rubbing issues will be apparent right away. I'd suggest trying it both ways. A big part of customizing is trial & error and just figuring out what works best for you.