Really, my best advice (and take it for what you paid for it
) is to start slow, know your budget and stick to it, and utilize as much free and cheap advertising as possible, especially in the beginning. Word of mouth is great. You sound like you know your niche, so that's a definate step in the right direction.
If you want paid advertising, I use
www.google.com (adwords) and
www.overture.com and both are doing pretty well for me.