I'd say your safe at 30k 

I'm not an attorney and Washington state law is a real pain in the a$$, so I'd recommend contacting a WA attorney that works with investors such as : http://www.seattle-realestate-lawyer.com/Do you have any "boots on the ground" in WA? 

Adding a 500k house to the property would put it into the 2m price class (was my retirement plan) at that point I’d sell it with around a 1.5-1.8 gain on my actual cash invested and the only people who would be able to afford it would be the Wall Street bankers that wouldn’t put their kids in the school and wouldn’t stimulate the local economy.

I'd reglaze it professionally or do nothing.

It has a really low mortgage rate that I'd like to hang onto.  

I’d say define your criteria for if you want to start smaller or immediately go larger and that will help dictate the types of strategies you need to employ. ie going it alone and buying smaller or needing to partner and go bigger.

I'd much rather be placing calls than sending mailers.

While my home is new, I'd like to maintain it well, and I plan to do this with all of my properties because I like taking care of my possessions. 

Even if you go the private money route that you mentioned (which also makes sense) - I'd advise speaking to a few HMLs at least to get comparable "market terms"

We have an appraisal gap but I’d rather not have to fork over that capital so I can do some minor remodeling and there’s still a possibility our gap may not be enough.