Your direction really depends on budget and what you have and what you want to accomplish. If you have big money, well, then you can do big things. Parts are getting harder to find. You may have to build your trike in steps. Step #1, get a frame. Once you get a frame, then you can start getting your parts. You can run a stock (non suspension) front end for the time being and pick up a suspension front end as time and budget permits. Once you have your frame, then you will need the parts, rear bearing carrier, rear axle bearings, steering stem bearings. You will need a rear axle and rear brake assembly- drum, brake shoes, springs and all your bits for the rear brake lever. You will need to figure out what you will do as far as a chain tensioner, stock or aftermarket. You will need a wire harness, start switch and head and tail light. You will need handlebars and risers. You will need a tank, fenders and seat which will fit what you decide on for rear fendes. You will need a grab bar and the fender mounts and hardware. You will need a coil. You will need wheels and tires and front hub. But frame first.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90