Ok so ya have
AoBR which is a great start!
From there the rule of thumb for orkz is more boyz... at least 2 boxes, that'll get ya 20 more boys & 2 nobz. Though you'll want many more as time passes.
After that perhaps a couple of Trukkz, 2 or 3 squads of lootas, and a herd of gretchin!
This would easily get ya on your way but when thinking orkz, you'll have to choose which way ya wanna go!
Green Tide, Kan Wall, Speed Freaks, Trukk/Wagon Spam, are among the builds one can make with the orkz. Search around Dakka to find some army lists & decide for yourself how ya wish your Waaagh to progress.
Just my 2 teef on the matter... enjoy your Waaagh & keep me posted!