Once you have two battlewagons, I'm not sure it's a green tide anymore.... But that's just semantics
So, having shoota Boyz foot slogging and sluggas in the wagons feels counterintuitive to me. Here's how I see that playing out: wagons barrel in, with waves of Boyz behind. Those squads will pile out and assault, and then the shoota Boyz will no longer have any targets! Whereas, if you swap them around, shootas in the wagon can pepper squads from safety, and slogging sluggas can assault when they get there!
I don't really like rokkits with shoota Boyz, because they seem interested in shooting different types of targets. Either wasting 18 shootas on a vehicle, or shooting two rokkits at infantry seems like a waste.
A
KFF big Mek might be fun in place of one of those warbosses- giving a 5+ to both the wagons and nearby boys, as well as an opportunity to repair the wagon, is pretty keen.
If you want some grots to babysit a point, I'd take out a single loota from each squad. In terms of casualties they can take before breaking, 9 Lootas is just as good as 10, and then you'll have 50 points for some grots and a runt herd.
Looks fun, though! Heckuva lot of Boyz to paint, but that's the nature of the beast.