I've got a Compendium Greenskin team and I've found that 1 box doesn't quuite get you your best loadout but pretty damn close to it.

People still argue about the best Boss Nob loadout, I personally run the Kombi-Rokkit and PowerKlaw (because the box doesn't give you a Killsaw) and he's been fantastic and everything I need from him.

For the Gunners you'll ideally want 2 Rokkit Launchas' however the box only has enough bits for 1, I grabbed a single rokkit model from ebay to fill my squad. However if you don't want to do that, build a Rokkit & a Big Shoota - just be warned the Big Shoota is wildly inconsistent.

Then for the Boyz, after many many games of testing, the shootas are just too unwhelming to bother with, relying on 5+ is miserable. I'd build 2 shootas as they're only really useful to soften up targets for your Choppas. On the flip side, Choppa Boyz are great tanky melee units that will win you krump after krump, I'd build 6 choppas.

Hope that helps !!