Greg,
My 182 is owned by an LLC that we formed for 3 partners to operate the plane. First, LLC stuff is State-specific, so you'll need to look up the appropriate information from the appropriate state agency (is the Secretary of State's office in CA).
You will need an LLC operating agreement. We combined our LLC operating agreement and aircraft operating agreement into a single document, though you can do them separately. We started with the AOPA template partnership agreement and modified it to suit our needs, then had it reviewed by an aviation attorney. As an LLC, we had to add several clauses related to the LLC operation. If you or any of your partners has AOPA's legal services plan, you can get one hour (each) of an attorney's time to review the documents. If you don't have AOPA's legal plan, I recommend getting it - it's very cheap insurance in any case.
One significant headache we ran into was the LLC registration and banking issues. In California, it takes a couple months for the LLC paperwork to get processed by the State, and you can't open an LLC bank account until all the paperwork is processed. Talk to your bank early in this process, and get it in writing exactly what they will require. Also, you'll probably need an IRS Employer Identification Number for banking/tax purposes. The EIN is easy to get, and can be obtained for free and instantly online from the IRS.
My recommendation would be to have the purchase of the aircraft made from funds already in a company bank account so that there is no question that the LLC is buying the plane, not the individuals involved. There are also a couple details on filling out the paperwork for the FAA registration, but they were pretty simple (once I figured it all out).
You should also talk to a Certified Public Accountant who is familiar with small businesses, or, if you can find a good one, someone who is experienced with aviation businesses. Get your accounting system coodinated up front.
Finally, and above all else, you MUST treat this like a real business at all times. Keep all the finances separate from personal stuff. Keep accurate and complete records, and have regular (quarterly) documented meetings of the LLC members. This is your only real protection from a legal standpoint. If it is an LLC in name only and you are operationally treating it like an informal partnership, you are a great risk of "having the corporate veil pierced" if any liability issues come up. I'm not an attorney or an accountant, and as I've said, I sought professional assistance to check that I was doing it right. Just trying to share my experiences.
I'd be glad to help you by sharing our operating agreement with you, let me know if you'd like to see it.
Talk to your partners at length about what-if scenarios. Be sure you're all on the same page. I'm lucky in that I think I've got a couple of really good partners who are also safe, conservative pilots. For me it has been a lot of work, and all the work has been completely worth it.
Jeff