I would take one step at a time. Get the stock ECU and engine running, get the bugs worked out, and then start upgrading.
Here's a link to a wiring/install guide for an RB25 into S13:
http://www.racebread.com/old/Documents/harness.swf
All it is, is connecting wires into spots that they normally should go. No magic to it, just getting some of the lower harness to work with the body harness. This was my first swap ever, and I took a guide and expanded upon it for others to use. Never did any wiring before that, so don't be afraid of it. The entire wiring diagram for the RB25 is out there and so are other wiring guides. It will save you from paying Carl $300 to do it and since he's swamped, it will also save his mind.
Luv ya carl!