It doesn't sound like you want to turn your freelance business into a body-shop of contractors/freelancers where you are the manager meeting with customers and

It doesn't sound like you want to turn your freelance business into a body-shop of contractors/freelancers where you are the manager meeting with customers and you have a staff of developers. So here's a counter idea - hire a really experienced developer that is looking to do some side work for extra money. Hiring a junior (or even a minion like junion) developer will have the overhead of mentoring the junior dev, extra time correcting work or explaining things about how you want them done. You probably want the least amount of overhead as possible because all of that overhead is your time, billable or not. Hiring an experienced dev that already has a day job on an hourly rate will give you flexibility because they won't be relying on your extra work as their sole income. They should also be a manager of one type of person - get stuff done, little drama or overhead.