You can't fit OEM 18s on the M3P, sadly.
I went with OEM 19s & Vredestein Quatrac 5. I'd suggest looking at rain biased rather than snow biased, consider how many days rain we get compared to snow... "Tyre Reviews" on youtube specifically made this point and pointed at the Quatrac 5's for the UK. Rain based doesn't mean they don't work in the snow, I beat a defender last year in 6 inches of snow - very satisfying! The all seasons were easily up to the job.
Camskill have a good choice right now. Excellent service too.
Yes email Tesla - they are about £320 each for the wheels. They were very helpful. And at that price - good value in my opinion.