First a huge welcome to Trike Talk!!!!!
A pal of mine is a double amputee so we had to make his ole Harley trike all hand controlled. What we did is got an over sized master cylinder and an adjustable proportioning valve
We picked up a single inlet/dual outlet type proportioning valve. Came from the master cylinder down to the valve and then out to the dual disc rear and out to the front. We then cranked the proportioning valve all the way in, test rode it, brought it back and started adjusting to get the correct front braking without sliding the front wheel. It took some time however it has been working now for about 2 years with no issues at all.
Many states however, do not allow adjustable proportioning valves so you might need to check with your state.
His trike has dual disc front and then disc on each rear. Work out great!