Thank you guys for yor input. I'll try my best with this and if doesn't work I'll try something different.
I'll post some pictures as soon as I start.
Just shooting blanks here, I was wondering if 2 RX 18 can be connected somehow and let one with a batteryhandle the 2 main motors and the other one with another batteryall other electronics.
The RX 18 schematics looks very detailed (thanks YHR), probably if I'd know anything about electronics I could use that information better.
Another question came to my mind : if I don't use smoke, sound ir is it possible to use those channels for something else without modifications?

Thanks again everyone!