IIRC you can no longer buy miles if you dont have North American address. Not sure if its billing address or Mileang Plan address. So if BTS as listed in your FT profile is correct you wont be able to buy miles
I found the thread. It seems to indicate no bonus miles promo purchases, not sure if it applies to regular non-promo purchases
http://www.flyertalk.com/forum/alask...s-no-more.html
If the above does not apply there is no annual max that i know of just a per transaction max (currently 40K) so one would have to make multiple transactions