Hi K,
Don't know for sure, but I'm doing what you propose. Didn't do market research, just jumped in. My niche is girl-girl anal and that's what I mainly shoot but, still, when I get the urge, I shoot anything I want.
Like Katja Kassin -- I love her anal scenes with guys, so booked her doing that -- after I had booked her twice for girl-girl scenes. But, yeah, for me the thought of dealing with 5 different site just sounds like a royal pain in the ass, so I'm going with my gut.
I'm doing well, too. But it took me three years to get here. So, I don't know shit really. I just know I'm slowly but surely building a megasite. It's medium-sized now, but every week there's more content, more members. Just going with what works for me. If you're in partners with a developer who handles site design and backend database work, multiple sites might be the way to go.
Kesey Seven
www.webelez.com