Bar ends are IMO the best on a trike, with the way the handle bar sits in your hand they are in a perfect position to use and you can get a feel for which gear you are in,
I have ridden a trike with twist grip shifter and wasn't impressed (this was before I got the GT3 with bar ends, so I wasn't predisposed toward bar ends).
Normal setup brake wise for a trike is a lever on each handle for that side front wheel, rear brakes aren't required (under heavy braking there will be negligable weight on the back wheel, thus it will lock up easily and not help greatly) and if fitted should have the lever some where it won't get grabbed by mistake as it can cause a trike to swing sideways and flip.
I have read of several mechanical setups with brakes linked to a single handle and I think Green Speed sell a suitable handle.