Taking pics of things like the roof, the windows, the plumbing, any stains, foundation, basement, and major ticket items  is critical. 

So in that regard this number is foundational.

The house is in northern CA, ARV roughly $390,000-$450,000, currently worth $200,000-$250,000 as it needs a lot of repairs ( foundation, roof etc...).

Should I first establish a trust (or legal entity) of some kind as a foundation to buy all my future properties in its name?

A first important part is knowing your type of foundation, and what if any reinforcing will need to be done for the area that will be exposed from the stairs running along it.

Also, I bought a foundation on a beautiful lot where a home burned down.

Lots of BRRRR people have a hard time with that because they want to stabilize the property and get away from the hard money guy.If you want to refinance it <6 months, go with a portfolio loan that's a little more expensive, but doesn't make you comply with conventional guidelines.You can get a 30 year fixed on  a portfolio loan and if the property's numbers are right (meaning you bought it at the correct price point, rehabbed it using some sense, didn't run into costly repairs like crumbling foundation, have the property rented at a market rate that sustains the property at at least a 1.2 DSCR and have decent comps) you should be able to refinance it at 70% loan to value using the new appraised value.Stephanie

Since it is in the basement and there are 4 trees lining up next to the property, I am going to have a structural engineer inspect the foundation to see if we can find the water source.

., need roof replacement, foundation issues, etc.) you can compete in a less competitive part of the market.

There are a lot of things to look out for like utilities, infrastructure, foundation, structural integrity, mechanicals, permit fees, contingencies, interest reserves etc.I would be happy to discuss more offline.