just get a LHD harness from a junkyard or Ebay man.... your asking for trouble otherwise, IMHO.
Once you have the proper length wires, it should all plug and play without an issue. Its probably just a little confusing right now with everything being opposite to what it looks like. Too early to panic!
The aux fan is different for the 6cyls, but i presume you have one from your M3... it should work no problem.
I can't recall off the top of my head the normal temp thermostart... 88'c I believe??... the only reason I run the lower temp thermo and switch is because I deleted my engine driven fan. If you are still going to run the engine fan, I would not worry about it.