I myself have been shying away from the thought of using battlewagons these days since everyone seems to be blowing them up as easy as they blow up trukks
They still have their place in the ork armt
ofc, holding more boyz, working better with shootas in comparison to trukks, the front av14 is invulnerable to peeshooters, not to mention tankshocking people and landraiders with the deffrolla).
But since you are going for a BW themed army, i'd drop few of the big shootas on the battlewagon to add an extra boy (with big shoota) in the wagons themselfs, even though you are paying more for less dakka, the overall efectivness will grow since the boyz squad will be bigger and you wont lose 2-3 big shootas automatically when you lose your battlewagon
i'd probably even drop all the big shootas from the BWs to fill up the trukks aswell, maybe even drop down to 2 BWs and add 2 more trukks ^_^'
(and belive me they pop like popcorn since the opponent WILL focus them down as early as posible since an unchecked deffrolla BW is just crazy)
Also regarding the lootas.
IMO they work best in squads of 5 , since with smaller squads you can split your fire, have a bigger average amount of shots (since you roll more times to determine the No. of shots) and can go to ground (not fearless, as can your squads) and furthermore they can't wiped them out completely with one ordinance or one flamer hit like when you have bigger squads (the only drawback is when playing Purge the Alien, since this way you bring more kill points on the table, but they still retain their upsides)
So if it were me I'd split them in to groups of 5's
Thats my thoughts on the list. Hope it helps