17 or 18" rims with dedicated snow tires - don't wring your hands too much about which brand snow tire to get. All of the standard top tier companies have comparable snow tires - bridgestone blizzak, Dunlop winter sport, Pirelli scorpion etc. etc. I have driven most of them over the years and really didn't see a difference. You could pick up a used set on here, Craigs list etc. or buy a replica set with tires from tire rack or one of the other sites.

If you are concerned about mileage, any summer tire will have the least tread life. You could go 19" all season for longer tread life (if you are planning on getting a winter set anyway) but may sacrifice some handling depending on how much you push your X. Michelin latitudes get good reviews here. A friend of mine in the tire biz is raving about Hankook Ventos all seasons now.....but I don't have any experience with this brand.

Good luck and enjoy the X - winter is a long way away