Yeah. Rule of thumb. If you saw however many weapons you're putting on your character, on a high quality model, and you wouldn't think it's stupid, go for it. So if you're a devastator, and you have two heavy bolters, it might look severely stupid.

As for wargear limits, I won't impose any. I trust you guys won't be idiots and give someone a thunderhammer, powerfist, mounted with revolving plasma pistols around the wrist to negate overheating. Keep it reasonable to fluff, and your vision of the characters.

TL;DR use a frost blade, just don't also bring two more to wield in each hand and his mouth, one piece style.