I wouldn't bother opening an LLC just for single family rental properties unless you are really determined to do it. Adds a lot of expense to maintain the LLC and you risk paying a higher tax rate. Some states can charge $1000/year just to pay for the LLC fee. You also have to get mortgages in the LLC name which will be difficult and eliminates most of the 30 year low interest loans available. Lending to an LLC usually puts you in the commercial loan side where the rates and terms are terrible.
Most states do not honor single-member (only you and a spouse) LLC's and treat them as if they are personal assets anyway so people pay all that money and headache to set them up and they do not even protect your personal assets. The lawyer guru's that push LLC's for rentals never tell you that little bit of information and since lawyers are the ones that make money off of setting up LLC's they want you to get a bunch of them.
Consider umbrella liability insurance policies to cover your personal assets, etc. You can get several million dollars in protection for only a few hundred a year in cost and you will have insurance company lawyers fighting for you if there is ever a claim.
If you choose to go the route of setting up an LLC, you will have to do it locally to the property that you are buying. Most states require that out-of-state LLC's register with that state which means that you now have to pay two yearly fees (the state the LLC is registered in and the one it does business in) instead of one.
If you go the multi-family route that is another deal, setup an LLC as they are more of a commercial business and should be treated as such.