I'm very good at running comps and determining rehab costs.

Whether To file a 1065 partnership return or being treat it as a disregarded entity, Is the determination based on the location of the property or the owners' residence state?

So, normalize those values, the state each year will determine the ratio by which the assessment differ's from today's values.

The after-repair value determines if the property is a good BRRRR or flip.

But if you are determined to do so, try to go for turnkey properties on the newer end - less maintenance which is good when you are investing out of state. 

I'm looking at investing in several out-of-state markets (potential BRRRR strategy in mind), I have a list of qualifiers that I'm sussing out to determine viable markets but would love to know: what data helps in determining a good market to invest?

The next objective after locating a target market, would be to determine if your primary goal is appreciation, cash flow or a little bit of both.

1.Zoning and Land UseUnrestricted Areas & Mobile Homes:How can I determine if a piece of land is in an unrestricted area or suitable for placing a mobile home?

And, the buyer cannot hire their own 3rd party inspector to determine those issues.  

With ADU's being so new and in most cases it being done for an owner who has no intention of selling, there are few data points for appraisers to currently use when determining the value of a home with a detached new construction ADU.