Save your dough... as much as you possibly can. It took me 2 years of constant worries until I was comfortable enough with my list of clients where cash influx wasn't even a worry.
Invoice immediately and keep good books. There are quite a few agencies I have worked for around here that will easily go 90 days out on an invoice even with calls to HR. Last summer at one point I was waiting on $23K in invoices between 2 different agencies and a production company, and I'm a one man show. So save your money and learn to absorb those times.
Don't short yourself on rate either because "you're just getting started". Know exactly what freelancers in your field (and area!) are making and stay competitive. If you start going down too low, even though you can save the client some bucks, they start wondering why you don't charge as much as others and think you might be a hack. So in a sense, trying to get the job by reducing your rate may hurt you.
Remember, your time is now billable. If you have to render, you're getting paid. If you have to transcode, you are getting paid. Just because you aren't "working" it is time that your system is being occupied and your time is being held up. Don't do stuff for free. I'm not saying if you have a big comp and you render overnight to charge them for it but if someone delivers a drive with P2 or something, you have to log/transfer it before you get started, those few hours are billable. If it's stopping you from working on other things, it is billed.
If you are doing day rate, don't ever except anything under half-day rate. If you work for 2 hours, half-day rate. If you work 5 or more, full day.
Have fun... being solo is the best thing I have ever done for my editing career. Much more freedom, more variety in my projects and a lot more money.
PS... welcome to the wonderful world of tax deductions now. You can deduct pretty much everything now.