XK 2006 wheel spacers

[vroom_vroom]

Hi, I'm due to pick up a 2006 XK convertible with the xk60 kit and 20" Senta alloys, I would like to add spacers to get a better stance and fill out the arches.

What is the best set up?
I'm thinking 20mm back and front or 20 back and 15 front?

Shoud go to 30 mm?

Where can I get a good set with reasonable price ?

Has anyone done this? If so could you share before and after?

Many thanks indeed

Im super excited

Affy