In Japan back in the day you could take a skyline in and get it rom tuned on a dyno for about 50000 yen ( 500 bux) As soon as you changed anything you would have to get it changed again.
As long as you built it the way it was going to stay you were ok..... My suggestions would be go with a standalone. The plug and play computers are usually designed for the car the engine was in so wiring knowledge and know-how is necessary.
A standalone that uses it own sensors like halteck, SDS ECT is what I recommend every day of the week.
With that said im using the HKS Vpro. At this point I'm very impressed with its capabilities. Only one draw back is it has to be tuned by a trained HKS tech. For that reason I would not recommend it to anyone unless you have access to one and are friends :>