I will suggest on forming the LLC now so you have liability protection right away.
If you do business with customers without it, you may get in trouble later.
The expense on starting a LLC is not too much.
The most important thing to do is figure out the exact business you are in and if forming an LLC is the right way to go. From your explanation, an LLC is probably the way to go but you don't need to form one right away. It might make sense to get some clients first and then form when you have the cash coming in. The reason is that an LLC will cost between $300-$600 to create (if you do it on-line) and a minimum tax of $800 per year, depending on the state ($800 is for California).
There are several sites that will walk you through the formation process. The one I used was http://www.nolo.com. It worked out pretty well.
Looking at things from the other direction, you might find The Top Ten Legal Mistakes of Startup and Early-stage Companies helpful.
Additionally, you may be interested in Can I form an LLC without a lawyer? (BTW, was born and raised in Detroit, but came to CA to attend law school and stayed.)
Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.