My thoughts on Linked In? Totally annoying to me, and I am so tired of people sending me invites to their network, or however it works. I must have an account I made years ago and forgot about, or maybe they just invite anyone they know. But that is just me, others may love it.
Honestly, I would find a way to get more clients from the five you already have. To me, they can be the best and effective advertising you have. Obviously, you don't want to badger them about it, but there must be some way to let them know to put in a good word for you with their colleagues. I can see where some would think that more business for you might somehow translate into their accounts not being worked as well(there are always people who think like that), but I still think referrals are always best.