I looked at that, and it means my spine would be banging on that support beam all the time, so I ruled it out.You could put the rear seat support the other side of the chassis rail if that gives a better seating position.
It may be a good idea to have the return idler on a radial arm centred on the same 12mm bolt as the drive-side pulley.
There are other ways gaining favour for the return idler ?It might also be a good idea to have both these things able to move left & right to accommodate the shift from low to high chainrings (I don't know).
Yes, its early days and a bit of a "look-see" excursion.You may have to add some adjustable stops for the turning angle of the front forks ?
Why you ask .....
Well your tyres are not smooth and those lumps on them may seriously divert the chain from it's chosen path , this will most likely occur when manouvering the trike and trying to go backwards ?
Now backwards is not generally a direction you think you need chain keepers for !
It happened all the time to my iLean FWD bike/trike and the tyres looked like this :-
failed to ever ride it , in bit's awaiting further inspiration ?