Idk if this was mentioned, but I'd put a line of wood down the center through the whole bus. The middle receives the most traffic and so h want the strongest support possible. Gaps will stress after a while. Just my opinion.
I think I would not use any sort of engineered wood for the sub-flooring. It will probably never give you any problems but it doesn't do well if it gets wet.
Instead I would have used a marine grade of plywood.
I too think it would be a good idea for more support down the aisle. I think it is particularly important since you are using an engineered wood product for the sub-flooring. Inherently it is not very strong when it comes to flexing.
Looks good! You should make a build thread and put your progress updates there. It'll be more satisfying for everyone watching to be able to scroll through your progress. No comment on the wood placement and floor, as long as your rigid floor insulation is the same thickness. But I do things half assed.
Looks awesome good to see progress, I used 2x2s 24" on center with ridge foam, then covered it with 3/4" TG OSB. I am a big guy and zero problems with floor flex. The OP looks like he used 2x4s 12" on center with maybe 1/2" osb, I don't see the OP having any problems with floor flex. Just lots of fun cutting all that ridge foam to narrow strips.