Thats a really strong list. Good idea dropping the koptas they suck balls. I would drop the entire nob biker squad, you could get yourself Deffrolas, weapons and armor for your BW's and Some much needed Lootas. Make sure the Bw with the mek is in the middle so the others get their 4+ Obscured. A Killakannon is probably not a good idea for these since you always want to be moving 12" since there transports. I run my BW transport with a KK though. Some Big shootas would be nice to have extra weapons on incase you take a WD result. Armor plates i like, most disagree. RPJ is a good idea and so are Grot Rigger IMO.
Hope this helps,