If you have access to small rare earth magnets and a pin drill, you could magnetize some of the models and keep your options open. In a small game, Nobz can be a powerful unit, but at higher point values, you'll face more elite enemies which they may struggle against, so magnets would give you flexibility to re-tool the unit later.
I think the WAAAGH banner is a must in any case - hitting WS4 enemies on 3+ makes the buckets of attacks Nobz have even more effective, especially if have a big squad of them. Plus, it enhances any characters who join the unit too. A boss pole is also a good idea.
Personally, I like a mix of weapons - one PK, one 'uge choppa and basic weapons for the rest. This gives you some high strength and low AP as well as a good volume of attacks to take advantage of WS5 S5 5 attacks on the charge. This gives you an option to assault and destroy medium armor as well as most enemy units.
You don't need too many PKs because you want to be locked in combat on your opponent's turn to avoid getting shot up. Ideally combats should last 2 rounds; the turn you charge and your opponent's to mop up (and set up your next charge!) - if you kill them too fast, your relatively high priced unit will face the wrath of your opponent's guns. If you expect to face some horde type armies (Orks, Astra Militarium, Tyranids) a kombi-skorcha can help thin the enemy ranks to avoid getting bogged down too long.
Using the parts in the kit to build a Painboy is a good idea. I also agree that if you don't already have Nobz for your existing squads, this should be the priority.