The main purpose behind an LLC is to separate assets to limit liability (hence the name).

@Leo HurtadoTexas and California both have a requirement of filing a separate LLC tax return even if it is a single member LLC.Are you open to working with an accountant remotely?

Finish the basement into a 1-2bedroom apartment with separate entrance (probably called an in-laws sweet, but you get the point).

I don't know how banks are about doing that sort of thing nowadays, but in other times it's been common to have an initial mortgage at a certain rate, and get a 2nd mortgage that is completely separate, but is a long term loan as well.

It's hard to separate the dangerous ones from the not dangerous. 

Is it a good practice to place each investment property under a separate llc?

It's a separate service to pay for.

You also want to make sure each property is help in a separate LLC.

I have a P.O. box set up and listed on the lease as well as a Google voice number and a separate email.

We were going to try to find a house with a single occupancy separate entrance accessory apartment.