You really only need the EFI-Main relay and fuse out of the AE82 fusebox. The fan control relay can also be used but not really worth keeping an entire fuse box for 2 relays.
Just buy fused relays and put them where it's most convenient. It doesn't hurt to go overkill with wiring by putting in a 4 or 8 circuit fuse panel in cabin to fuse off ECU, gauges, boost controller, new ECU, whatever else might need power.
Get and make a 'fusebox' if you feel you need more relays. Keeps it neat and you can stack more on later if you feel the need.