How continuous is your cash-flow?
Are you living by the seat of your pants, or are you able to put money away for a time, and build up a buffer? Personally that it what I would be looking for, then take someone on, with that safety. You'd need to make sure that you have enough to keep them busy though - so you'd be looking to land a reasonable size contract before taking the plunge. Do you have in between large jobs work that you can give them? Might be worthwhile chasing that, or setting up a number of customers who are interested, but explaining that you will launch at a particular point in time. If you offer them a better deal, you both win, and could overcome your potential cashflow issues.
The other alternative is to take someone on initially on a per project basis, might cost a little more, but overcomes the cashflow issue.
What you need to be able to do is systemise your business - make it so that it is a cookie cutter, and can be repeated. You need to be sure that you have instructions that can be easily followed, and then when you're ready hand them over, so you can concentrate perhaps on getting more work in?
How well set up is the rest of your business, the administrative side? Who currently does that? Could that be the first thing to outsource / offload, so that you can continue doing what you are good at? What about the day to day operations? Do you have your accounts all set up and clicking along? If you don't you're going to go through a lot of pain and expense if you have staff.
Don't take this the wrong way, but you sound like you need to get to know your business a little better before trying to expand, or at least find people who you can pay to help you, but don't actually work for you. If everything is ticking along, and you have plenty of work, you wil know, as it should be easy to transition.
Another alternative would be to partner with someone who has what you don't, and work together, or take on a partner who will generate their own money.