Rental property and umbrella.

I would assume at this point you at least have an umbrella policy if you're not using an LLC to have  a little personal protection maybe and this would be where your question seems to fall in line more.

I've been thinking umbrella insurance..

If they don't have proper STR insurance and a decent umbrella, you might be at risk in case of an accident. 

Umbrella companies also

I'm now just paying about $1k for my taxes and insurance (including super expensive earthquake and umbrella liability policy) which are essentially my living expenses.

Yes you can have a Master LLC and each house goes under the umbrella of the master.

If you're going the umbrella insurance route, make sure it will cover you for several things including just the routine slip and fall (like mold or earthquake).

LLC’s are not eligible for residential loans and have to get commercial loan product.There are plenty of discussion threads on bp about pros and cons of a LLC, and how to try to do a hybrid (which I’m not for).For asset protection, just keep your property in good condition and get insurance including umbrella liability policy

As you can see from the 1000 other posts on here about whether or not you should put your property in an LLC posts.. an LLC is just one "layer" of protection but a good insurance policy and an commercial umbrella liability policy should do the trick.Hope that helps!