There are also additional costs of operating and maintaining an LLC, like separate bank accounts, annual report filings, tax filings, etc.2.

That one is a big deal for rebuilding.I've also heard of property tax reductions for properties significantly damaged during the storm.Depending on the property and what you want to do, the hurricanes affected property tax, insurance, and permitting in a lot of ways.

It's a balance of cashflow and wealth accumulation.One of the goals is to have tenants pay as much of your cost-of-ownership as possible (loans, taxes, insurance, etc.)In high-cost areas, any Class A or B property you buy will usually negative cashflow for the first 3-5 years, until rents rise enough to cover the negative cashflow + rising taxes & insurance.Investing OOS increases your risks because you may not know the market and you can't check on everything/everyone all the time.If you move forward with your buddies, HIGHLY recommend creating a solid Partnership Agreement!

Does he understand, Deeds, Due On Sale, Insurance, tax implications, servicing, contracts and so on?

I assume your prop tax increased 1.1% to 1.2% of the ADU cost even though the ADU only valued at $75k???

After closing, when the property taxes were due I never received any bill.

I recommend that you look at Notice of Defaults, Vacants, Tax Liens or Probate. 

As more people placed more properties in STR inventory, and as more municipalities taxed and regulated the industry, the profitability of the overall industry has reverted to a much more aligned (lower) risk adjusted return.  

Keep in mind taxes go up as do rents.

Technically it would be best to get a C Corporate or S Corp. to flip properties and since you are considered a dealer if you do several properties a year and this could have negative tax consequences in an LLC.