You may want to test and see if the single smaller 5.75" diameter light puts out enough light and in a pattern you like before going full bore.

If you plan on running a hign beam bulb in the low location, it requires no changes to the wiring system, as the low socket has a wire for both high and low beam modes.

Wiring in a relay system to power them is a good idea. Plenty of voltage drop in the OEM harness/system.