I don't really get why you'd want to engine swap a 3 door when it's cheaper and insurance friendly to buy one where the SR20/GA16 is standard on it. Yes it's possible but a waste of money.
If you really want to keep the Si then transplant something interesting.
As for wiring, the pin-outs won't match so unless you're prepared to Frankenstein the looms, you better get all the chassis wiring, dashboard loom and ECU too and not just the engine loom.