Failure to take these measures will leave you vulnerable to a plaintiff’s attorney interested in piercing the corporate veil.

I am  starting to evaluate deals in the Pierce County, WA area, and I see that there are some opportunities for houses in pre-foreclosure.

Welcome Pierce.

Piercing the veil on a typical single-owner LLC is something that takes a plaintiff's attorney 3 months out of law school about an extra hour of effort.

If you are out there screwing people, they'll find a way to pierce the corporate veil and get to you personally, LLC or no LLC.  

You need to keep each account separate or you risk commingling funds and piercing the corporate veil. 

This means that you will probably need to pay registration and filing fees in at least 2 states if you don’t buy CA property as a CA resident.Any lawsuits should be limited to the assets of the LLC and not your personal assets (assuming you run the LLC appropriately and the corporate veil is not pierced, some debate as to SMLLC).

Get an insurance policy - especially if you have a mortgage on it or self manage - LLC can easily be pierced if either of the above is true

Commercial brokerage is much harder to pierce but more consistent inventory and unless  with bigger pay checks in smaller markets.  

Regarding liability protection- There are protections provided by having an LLC, but a good attorney will find a way to pierce your LLC if they know you have other assets.