Use a tray mounted hitch rack which usually has a 50-75 lb bike per tray limit. On that model prius, installing a hitch rack is as easy as moving the muffler out of the way and tightening a few bolts.
Could be chain slap or chain skip. You are supposed to avoid the small/small and big/big combos to prolong drivetrain life. Small/small at high power will wear it out at an accelerated rate.
You can get most of the ebike made in north america (frameset, drivetrain, wheels) but sourcing things like cables, connectors, chains, tires, and tubes will not be easy.