Battlescribe is wrong about that, a nob in a boyz squad costs as much a standard boy. Each unit that can have a nob doesn't pay extra points for upgrading a dude to a nob.
Big choppas for nobz are a solid choice, many players prefer them over p.klaws.
Overall your list looks ok, just one thing should be fixed, the tankbustas unit. Now I assume you mistakenly wrote 19 + nob instead of 9+ nob which is the unit you have with 170 points. I'd suggest to split that squad into two units of 5 bustas, this way you can thow 2 melta bombs if you need to do it, and you also gain a wound (a second nob). They both can ride in the same trukk. Add a couple of bomb squigs to those units if you have some spared points.
I also see some confusion with the points costs of some units: the nob with waaagh banner is 79 points, unfortunately he comes with a kustom shoota (4 points) which is mandatory. 30 boyz, nobz and big choppa are 189 points. The warboss is 68 with your loadout. The big choppa costs 9 points, not 6, that's the issue. You can drop his kustom shoota for a regular shoota saving 4 points.
IMHO a list like yours is ok for an ork beginner
2000+
