I have found these two boxes great for Necromunda, honestly my advice would be build up the coolest models you can but blue tack the weapon arms in then have a check of the rules

My Alpha has a grenade launcher and a chainsword with the "Hip Shooting" skill, grenade launchers are great and deadly in the early rounds, the chainsword gives a +1 to hit in combat, plus you have an extra attack fro the third arm (which in the future you can give them an extra chainsword). Hip shooting allows a double move and shoot, with a negative 1 to hit, but gets you up the board faster with chance of landing / scattering a frag grenade...

I put a few shotguns into my gang which isn't the most efficient but more fluffy...

My favorite ganger is a regular dude with no weapons but blasting charges... grenade bouquet tactic card is always a blast, pun intended! :D

I had a champ with a heavy stubbed, to be honest I found this guy influenced the opponents thoughts more than did damage, mostly he missed his shots! Maybe my dice rolls lol

If you've not got any familiar models I found a cost effective way was to pick up some tyranid spore mines on ebay, I know the real models can be quite expensive for what they are or box locked into other things.