We’ve also found that at least one of the authorities (Jefferson county) started to run some kind of property specific rental comps which can also affect the max they’re willing to pay. 

One of the first things you should do is to check the HOA rules to see if they allow STRs.

In one town where we had 12 rental houses, every one was sold to owner occupants, not landlords.

Then hire one that sounds competent and that you can get along with.

Or should I find a property first and hope that no one will get that property under contract right away?

My number one question to any agent would be do you invest in real estate. 

A question we faced was the exact same: Should we buy used appliances or go for new ones with warranties? 

I was definitely on the fence about this one for a little while before making the purchase, but there were a number of attractive features that ultimately led me to move forward with the purchase.

@Luke Spencer I am not on the management side but I can tell you it took 2+ years to fill 300 units at one of our facilities and the other just hit 300 units in 12/13 months so it really depends on the demographics, and local housing market trend, the more people moving in and out the higher the demand for storage.I think if you're looking at a saturated market then the upfront cash to turn the warehouse into self storage is not a good idea but then again, maybe those operators are on back roads ( low visibility ) and don't push google ads well.

Out of the four properties , there is one solid tenant, the other is struggling and the last two  properties are not renting.