Start with 2 running cars if it's for first swap. Photo/video everything and write down everything.
What I have always done for any swap is get the ECU/wiring out of the donor car, label/document all the connectors, and with any wire cut, label both sides!
Then when the ECU and wiring out of the donor car. Plug it back into the engine and get it running. If it doesn't work you can go though anything you cut and have both sides. You can hook it all back up until it fixes the issue.
Then with everything hooked up in the recipient car get all your measurements and wiring labeled while it's still running and you can test things. Don't do anything to the wiring in the car yet.
Do the mechanical transplant next. Get it all in, plumbed and read to run. Then get it running with the unmodified hardness from the donor. It should work the same as when it was in the other car. Fix any wiring/fuel issues first so it runs fine.
THEN pull the wiring out of the recipient car and merge the hardness.
By doing it in stages and keeping it running at each stage you can reduce the possible issues to troubleshoot.