market research - where to look

Hola,
I've found my niche and have been building a website for it going on 2 months now, and it is coming along nicely. However I need to familiarize myself with more of the business aspects (right after this I'm going forum browsing to see what other subjects have been discussed in this category). The main focus right now is how much of a market is there, and where to set my goals. What I figured I could do is get the gross income of 4-5 of my competitors to give me a estimate of how much of a market there is. Question is, where do I get these figures. I thought about calling them up for an investement package or something along those lines. But I really don't want to tip them off that I am coming =)

Thanks for any help.
webG