If running a line from tank to racor and then to engine, it depends on the length of the run and how many fittings and valves are in the path. Without knowing details of such, I would go with 3/8" ID hose and that should be fine. 1/4" probably fine (yes on the engine they already use this), but going some distance to the tank under suction it is better to size up a bit.
Racor fittings readily available in NPT fittings, then get an NPT to hose nipple fitting.