I don't know if this is any help, but I bought some Thompsons this weekend to stain my deck, and they are giving 4 bucks back for every gallon purchased. http://www.thompsonswaterseal.com/news/promotions/deck_days.cfm It made the hard work more bareable.
as much as i wish i didnt i would agree that consulting a professional would be your best bet. a pro would be able to view the space to be painted and make a more accurate assessment of what should be done and what product should be used. in my experience with my local indianapolis painter i was able to have a professional consultation, a free estimate and a quality job. i would guess there similar companies in your area that can help you in the same manner. saves headaches and time!