The struggles of a small company

Going through this process myself now, I have a renewed respect for anyone who has built their own company. You start off just by yourself, if you don't log hours you can't invoice and if you can't invoice you don't get paid.
But, you need to keep new working coming in. So, a portion of your time has to be spend on non-billable activities, such reading and responding to RFPs and otherwise trying to figure out where your next project will come from. I have a few different pokers in the fire right now, if all of them bare fruit, I'll be so busy I won't know what to do. If none bare fruit, I'll still be okay, but that'll mean the business isn't growing any.
So, do you get all of the work and then hope you can hire to get it all done? Or do you turn work away and hope that later (when the current work slows down) you'll be able to find more?
It is an interesting challenge. The next few months should indicate how I've been able to handle that challenge.