We have a nice, large lot (7500sf, level, no trees) in a prominent NR3 zoned location in Seattle, currently serving as a grandfathered duplex.

Read Beginner’s Guide to help you get started: http://www.biggerpockets.com/real-estate-investingI hope BP serves as a helpful resource for your REI endeavors!

One company owns everything and does nothing (this is your SLLC a/k/a “asset holding company”) and a completely separate company handles all of your operations (this is a traditional LLC a/k/a “operating company”) For the operating company which serves as your face to the world and through which you do all your business, you establish a Traditional LLC to carry out the operations of your investments.

What purpose does that serve? 

If your only goal is just to find more deals, then Loopnet serves the same function but for free.

However your situation becomes a trickier case study since these properties first served as your primary residence which could provide additional benefits form a tax perspective not available to an owner of investment real estate and nobody has a crystal ball and knows the property with certainty will transition into an investment property. 

They could've charged me for dog food and I would not have even realized it!

If you want to provide proper notice (ie: you don't get a response from a txt) that proper notice in Washington state requires that a notice be "served" Guidelines here: (also keep in mind that date of service is day zero)How to serve a notice1.

The combination of rotting food, rat droppings, and general decay was overwhelming.

It would cover any food that spoiled as a result of that.