Hello and welcome to the Club. I moved your thread to the Supra Chat section as you’ll likely get a better response here than in the technical section .
With regards to your car, are you sure it’s a 97 as I though the UK spec production ended in 96.
Also with regards to the changing to 18’s, I’d suggest you keep your stock 17’s to the side as these are starting to fetch anything from £600-£1000 in good condition. The UK spec wheels also have a little extra bracing located on the centres, and if you do ever sell in the future then it might be best having the stock wheels.
Another point to consider if you go for 18’s is checking for clearance of the 4pot larger calipers, although it’s usually down to the wheel design you choose.