I know it's over a month old but just in case.
For a game at 500, I like it.
Couple small tweaks I'd make:
The Deffkoptas work best if they are just left standard. The big bomb and KMB sounds good for 5 points but they'll do more damage with the extra Rokkits. I've spent ages trying to use the BB and it has never really done anything but push me to make bad movement decisions. The KMB is just a bad weapon on this unit.
I'd take the Power Klaw off of one of the Nobz and put it on the warboss instead. He is tougher, has more attacks and hits on a 3+ with a higher strength as well. I don't know what point you are at with relics but this also let's you take the relic Power Klaw "Da Killa Klaw" which would allow him to do more damage still because he would hit at his native 2+
I think the Kans are solid at this point level. You're putting enough toughness and wounds on the table for a cheap enough points investment that you can reasonably expect other 500pt armies to get a little overwhelmed.
On the flips side the boyz are going to die. There's nothing in the army providing a durability boost for them and they are a pretty frail unit. There's not really a good fix for that at 500pts. Just try to keep them in cover or on an objective and don't expect them to do to much heavy lifting.
For expanding the army to 1500, Orks do really well when they are up in the opponents face and forcing them to deal with multiple threats at once. Any unit that is decent in melee and has good mobility pairs really well with Goffs to get a lot of damage across the table really quickly.
