I have checklists for all the documents I need from the seller/ seller's agent and have a separate checklist for basically all the things an inspector checks plus a few others.

The garage is enclosed and basically a bedroom, there is HVAC lighting closet , separate door etc, but no window.

There is enough space to include a separate unit in the backyard. 

As a result, we had to apply for a new gas line separately.

As a result, we had to apply for a new gas line separately.

Pay yourself "rent" into a separate account to use for the property/future investments and get a feel for what the actual cash flow would look like.

Does anyone have a recommendation for either national or local lenders (I’m based in LA) that will include short term rental income in a debt to income calculation to help finance a separate conventional mortgage?

You can separate and protect each of your rental properties.

In Joshua Tree, your cannot STR two separate structures on the same parcel.

My W2 job means that I don't actually spend any of the profits from rentals, but they are all self sustaining and separate from my W-2 job and living expenses/mortgage on personal property.