The perfect wheel size is considered to be 15x6.5j ET37/ET38 If you going a lower offset, this will put the tyres closer to the arch... So its hit or miss, depends how low you are!
Id go for a TF035 Turbo Setup... Same as TD04 Flange Fitment Turbo Kits Mappable ECU... Try having a read at the Stage 1 Tuning Guide... Found Here: http://www.ukstarletowners.com/page/articles.html/_/tuning-walkthroughs/stage-1-200bhp-stock-engine-turbo-r35
Thermostat is mechnical... Opens when the water is at the temp its designed for... There not expensive put a new one in, its not worth messing about... EP's have 2 sensors 1 for the gauge and 1 for the ECU. Chances are the one of the ECU was the one u broke...