Usually this is not cost effective unless you are going to do extensive work on the property and as mentioned everything must pass inspection.

I know that I buy my properties in cash all the time (not on the market), conduct a BRR, and refi it within a couple of months (1-3) to a conventional loan. 

I would run some comps on the large buildings that sold in the past couple of years and reevaluate those numbers, especially your rehab costs.A quick note on the seller financing aspect: Most buildings that do sell at that 15-22/unit mark need extensive rehabs, are in terrible areas, or have unseen issues.

I have used the Syndicated Deal Analyzer available at themichaelblank.comIt costs around $200, but is a very extensive spreadsheet, and includes quite a bit of video instructions, which were worth the $200 alone.

I put extensive rehab into the property being sold.

Yes, having a non-permitted 3rd unit does restrict the resale value of the property, because you or a future buyer could be required by the City to eliminate your 3rd unit and by extension the income from that unit.

What are some of the most helpful and informative websites/online tools that you (rental property owners) like to use when conducting research in a new market outside of Zillow, Redfin, etc.?

Would you keep capex and repair budget that high even if you have done extensive repairs? 

Install downspout extensions (preferably under the ground to route water away)2.

@Andre' Arceneaux I made a post about this a little back and it was astonishing to see how much realtors dont respond (even to fellow agents like myself). not sure how they conduct business this way but good luck to you.