I think you're following the right approach. Start small, figure out what you want, and then commit to it. Although nothing locks you into a hotel program, I've learned (and the hotel programs have, too) that you're more likely to stay with a hotel group once you've joined their loyalty program. No reason to commit yourself to a group when a little preliminary investigation and research might convince you that the program is not worth your while.

One more reason to consider multiple programs eventually, however, is the way the various groups run their quarterly promotions. As I mentioned earlier, SPG ran a fine promotion for me this spring that meshed with my current travel plans as well as my summer vacation. Their current promotion, Triple Up, Double Up, is fine but not as attractive to me so I've shifted some hotel spend to Hilton.

Your annual spending amount will provide you multiple opportunities to take advantage of good airline and hotel programs. In addition to the hotel programs and cards discussed in this thread, I would consider taking both the Amex Platinum and Chase Sapphire Preferred cards. Each program allows transfers of their earned points into various hotel programs as well as a number of airline programs.