I found your first line intriguing, "I've been an agency recruiter whole time and I am done with it."
Why are you 'done with it?' Your answer to that question is key to determining if opening your own search firm will make sense for you.
How does your billing compare with others in the office (you don't have to answer that here, just for your own sake). If you are a top biller, even a solid steady 200k+ biller, then this could possibly be a good move for you.
If you struggle month to month to meet your goals and make placements, then I'd probably not go the solo route.
Another thing to consider is business development. Is that a strength of yours? You will need to bring in business consistently.
This is not a difficult business though to get up and running in terms of putting process and procedures into place and executing...staying on the phone as much as possible.
Regarding LLC....yes, talk to an accountant or attorney and ask them what makes sense. I'm an S-Corp, but when I started I didn't talk to anyone and forgot to mail in the form requesting S corp status which meant I had to be a C corp, and for me, that meant double taxation which wasn't ideal to say the least. :)
Another option to consider if you feel like you need more guidance and support is an organization like AgentHR which is a network of indepenent recruiters and gives you access to job boards and a database and you can do splits with people there. They take a cut of your placements, its' not a route I'd go, but it might work for you as it could give you resources that you can't afford right now and you pay as you make placements I think. Google it to see.