[P-hack]

You need to understand how to title a vehicle too. Even a salvage title in my state can be a PITA, for a few scratches. I bought a salvage bike, once, that was the last time.

Get a clean title, get it in your name, THEN convert it to a trike, and you are probably in business.

Get a salvage title, make a homemade trike, take it to the inspector to get it approved, and you might be pushing it to the junkyard.

An old thumper (with a carb for starters, can retrofit FI later) will get you rolling. 4 speeds would probably be adequate. I was getting like 100mpg on an old cb125 4 speed, carb, unmodified. Plus it was like $300