ballast resisters
Electric pumps should be AS CLOSE TO THE TANK as possible. "That is all."
This is oft-stated, even by Holley and other EFI vendors, but doesn't make it true. I mounted an EFI pump in the lower engine bay in my 3 Mopars. My 65 Newport has run that way since ~1998. Prior to that, I tried the "mount near tank", with much fussing and it is hardly accessible for roadside repairs. If you test it, fuel just pours out of the 5/16" factory supply tube (or should), so I can't imagine it restricting the pump inlet. Re "priming", someone here asked Walbro and they said their EFI pumps can suck fuel up to 5 ft high, so no concerns there (unless climbing a 20 deg grade).
You could power the EFI pump directly off the key switch (IGN circuit), but the current draw and inductive kick-back could burn up your switch, and the extra draw could draw down your ignition voltage, as others mentioned, making for a weak spark. Always smart to power via a relay (and fuse) from BATT+. You can tap BATT+ at the big stud on your starter relay (firewall).
Re your ballast question, it is to reduce the voltage to the coil when the engine is running. That wasn't just a Mopar thing. Many here changed to a newer HEI ignition system that gives a stronger spark and runs directly off battery power, hence no more ballast.