From my experience, a Plus 4 on Roadster wheels is over tyred for the performance. If you have time to reconsider before build Thomas, then think hard. Once it's built you can't easily reduce the wheel width.
Plus 4 is 6"x15". Roadster is 7"x16".

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4