I would only say dont buy for appreciation because at some point our 5 year run up in prices will stop.

I know the traditional advice would always be to start a business if you have a high likelihood of running it successfully. 

After the loan is paid off you only have $6,500 remaining ($82,500 - $76,000 = $6,500) to account for your cash invested.Given that you already have a decent interest rate (4.88%) I would not run the risk of a higher rate with the Refinance.This appears to be a good cash flowing deal.  

I would run the LLC and we would need to determine ownership %s

You will have a hard time remotely running 15 spaces  with the expectation of  a third part manager.  

I plan on keeping the property for the long run.  

I worry that people will be inconsiderate about usage, running partial loads while others are waiting, etc.

Water heaters in Az Run about $400-$500 (12  year warranty, 40Gal, $499 at Home Depot) , and I can install it myself

you may be running into the negative perception of wholesalers who tie up property with no means to actually close. and if they cant assign the contract they walk . 

Also I think if I compare equal amounts of hard work at my job vs. running a real estate investment business, I will make more in the latter.