wheel off sets help(non csl)

[s.mac]

please don't shoot me down

I have no idea how to work this out...
I've even used the off set calc but it means nothing

If I had a wheel 17" x 7 IS48
and wanted a set of wheels, OZ Ultraleggera.

and was told
17" x 7 et37

then someone else says
17" x 7.5 et40

both with 215/45/17"

or

18"x7.5 et45 with 215/40/18
what would you go for?

Mini cooper s latest shape, is it R56...I dont know not up on minis....