Thanks for the comments and reviews! I'm really happy with the car now, took a lot of investigation to work out sizes etc.
In the end I went for the below wheels, ordered direct from Rota...
(you'll have to go direct to get the same size as me, third party retailers won't do them, and may not even be able to offer the correct PCD)
- Rota Grid Drift 18"
- 5 x 100 PCD
- 9.5J Wide
- ET 23 Offset
In terms of running without rubbing and catching issues, you'll need 5mm spacers all round to clear the struts on the front, and the arch linings on the back. I'm running 5mm spacers on the front, and 15mm spacers on the rear. I have had the front arches rolled on mine as well, and trimmed the arch liners down on all four corners just to be safe - at the time I couldn't quite work out whether or not this was entirely necessary, but even now with the fronts rolled, the tyres do sit very close to the wings, so I would definitely advise rolling the arches to be safe,