Anna,
To answer your questions:
Priceline is good for either far in advanced planning, or last minute bidding. Their inventory changes daily, and I've seen availability for up to 5 months in advance, although that is unusual.
If you are starting to bid more than 2 weeks in advance, however, do not get stuck in the trap of thinking you HAVE to get your hotel the very first night you bid. When people do this, they often end up way over-bidding. Your best strategy would be this: First, reserve a room where you can cancel without any penalties. This way, you'll at least have a back-up reservation in the event PL does not have inventory for your dates. You can start bidding for PL as early as you want, but I think any earlier than 2 months in advance and you'll be wasting your time. Check
www.biddingfortravel.com for bidding strategies, including doing rate research before you bid and utilizing 'free re-bid' zones.
Try once a week up until 3 weeks prior to your trip; then start trying every 72 hour period. Be patient and try not to over-bid!
The star ratings are very accurate. I think there have been major complaints about only 5 properties NATIONWIDE. And PL will change a star rating if enough people complain to them (if not remove the property from their inventory altogether.) So I wouldn't worry too much about the quality. Rarely, rarely, rarely does anyone ever complain about being stuck in a dump. More often, people will complain that a 3* should be a 2 or 2.5* hotel instead, but most will acquiese that despite the disparity in rating, it was still a great deal for the money. Honestly, I think you could bid 2.5* and still be sure you won't get a dump. 2* seems to be the riskiest, but then it also depends upon what you are accustomed to. 2* hotels are usually no-frills places like Red Roof Inns or Motel 6. 2.5 are usually Fairfield Inns or Amerisuites type places. 3* is generally Sheraton and Marriott type places. And 4* is generally Westin or Hyatt type places (there is some crossover for the brand names of 3/4* hotels).
Hope that helps!
BK