I am in the camp of Topaz on this. Two engines on the trailing edge of the wing is possible but neither efficient nor easy to do. The licensing of the UL category is done through national authorities, not the easa, so what's possible in one country, might be a problem in another. Whatever falls out of the norm, will be harder to register in many countries. Maybe it works in CZ, in AT you probably will have issues. Looking at the regulations in DE, it is also not clear to me, if it works.Hello!
When I spoke few year ago with Crossover boys on AERO (very sympatic team from Portugal) I told them, that their airplane has big problem - two motors. No way to make certification. But situation changed - this construction is actually allowed so I hope we will meet again on AERO.
Look at Darek Lewek's Geko project. I think he solves many of your problems quite elegantly. He just spent too much time on it to make it really cheap (seriously: He did a great job).