You would need the relay set, on the 1995 Mustang it is a self-contained module with 4 relays inside, so not like the Ranger/Bronco setup with individual relays, fuel pump relay and EEC(computer) relay are the two required.
It's call the CCRM (Constant Control Relay Module)
In that year it would be near the overflow tank, hopefully it came with the harness, black box with an "S" or "R" or "?" on it
Inertia switch should still be in the passenger foot well/kick panel of the Bronco but not sure on the wiring from the CCRM to that cut-off switch.
High pressure fuel pump is needed, could be external, vs in the tank, depends on your current set up.
O2 sensors on each manifold and one behind the Cat converter, did that wiring come with new engine harness?
EDIT: oops, 1995 Mustang 5.0l(302) is OBD I so no O2 sensor behind Cat.
Not sure what you have for speedometer now but '95 Mustang PCM would use/need an electronic input from a VSS(vehicle speed sensor)
The benefit of "factory" electronic systems is in the computer management of those systems, so the sensors the computer uses must all be working to get the best MPG and daily driver reliability, and to pass emission tests

So adding power and grounding without all sensors connected would mean poor MPG and poor performance, so no benefit in EFI and electronic ignition.
If you want max. horse power and performance then you can use "non-factory"(user adjustable) electronic controls which require minimal sensors or switch back to carb and HEI which need no sensors but require adjustment to maintain best operation.
A properly working EFI system beats a carb system hands down, buy key words here are properly working.