All, I'm a Sr. Network Engineer with a full time job doing network admin, enterprise storage and virtualization work. Seperate from my full-time job I've got two different very wealthy clients that I've done work for previously, but I wasn't getting paid for, long story...don't ask

In my new role I'll be in a position to charge the clients for my work, but I'm not exactly sure #1 what I should charge and #2 whether or not I need to create a LLC of some sort. Most of the work will be networking, wired and wireless, VPN as well as some server administration. I'm thinking of starting at $100/hr. The work will be all over the US, but I'm based in Oklahoma. The client made mention that I could also be paid on a retainer basis whether I work or not. I'm not sure I want to go that route though.
Also, are there any example contracts that you have used that I could have the client sign which spells out the rates and the overall agreement for service?
I really appreciate any advice you have on this. Thanks in advance! I realize there are some existing threads on what to charge for work, but most of them are extremely old or not really for the same kind of work I'm doing.