I can't answer your questions about PRL's, but I can help out with the sponsor info.
Any amount of money donated makes you a sponsor, and that membership lasts for 6 months from your most recent donation. In order to become a premier sponsor, you must accumulate a donation total of at least $100 (although, due to a holiday promotion, you can become a premier sponsor by donating a total of $75 if you donate by midnight tonight). Premier sponsorship does not expire and you get all the benefits a regular member, a sponsor, and a premier sponsor get.
Hope this helps!
-Anthony