Get gov status as non-profit before soliciting for donations. Check local city for regs regarding solicitation by non-prof org (do you get a break off from the business license? does solicitation for non-prof license cost less? ect.)
Oh yeah, if you have gov status as non-profit you can get certain discounts, Chamber of Commerce in many cities charge less for such org than businesses and professionals.
Are you thinking of making money off from this? or are you just doing this for purely altruistic reasons? I don't know what it take to convert a non-profit or not for profit org into a for profit company, but I can't imagine that its easy.
By the way what kind of spiritual retreat are you considering? I'm a web designer, I'm open to the possibility of helping (Although I am a for profit individual) . If this thing has wide spread appeals, you can also easily take small donations via the web with PAYPAL. They have this neato feature to donates small amount with credit card over the web, cost 2.9%+.30 per transactions though, same rate they charge businesses.
You might also have a higher cost of startup as a non-profit org. If it were a private business, all ya need is a ranch, a business license ($50) and an IRS EIN number and you're in business. Of course there's the issue of higher taxes with being a private business.
Found that one while googling on the subject, it might help ya out.