First off, congratulations in identifying that a fully programable ECU is the right step to take! This is a giant leap for TGTT.com!
You want to consider a few things:
- How much functionality is required
- An ECU that is popular in Britain for better support
- Local tuners available to you
- Omex / Link / Emerald (These are all similar, I think Omex and Emerald use the same mapping software)
- Motec / Autronic (If you want to burn cash!)
There is no point in buying a Motec if you're going to be using the basics. You don't need to worry about harness' etc, it shouldn't be a problem to wire up - there isn't much required:
TPS, CTS, AIT, MAP, Distributor trigger / Ignition, Injectors. You may need to change some sensors to be compatible with the ECU.
There's not much else to it, most will require boost to be controlled by another device be it MBC or EBC.
Just make sure you go somewhere who knows what they are doing.