It's everything that comes after that which determines whether the property is worth pursuing in the first place. 

If we were to pay the $50,000 cost in cash, then our return would be 6%.This cash-on-cash return is easy to determine, BUT...Let's say I have a HELOC on my own house, and my mortgage is completely paid off.

As mentioned above, take a look at other properties that are similar and determine what they charge in high season vs low season, weekends vs weekdays, holidays, etc to give you a broad idea of the going rate for nightly rent.

Are there any local Columbus investors that can help me determine what makes it so attractive? 

Start by determining your exit strategy and running the numbers for that strategy. 

Have you determined what type of MFR you are seeking?

Some potential next steps:- Attend some networking meet ups- Determine your strategy (buy&hold, fix&flip, wholesale, etc.)- Pick a market to invest- Find a team (realtor/Lender/Contractor/etc.)- Start analyzing properties- make some offersHope that helps. 

Nothing happens to you if the tenant uses your internet to do something illegal.

To determine if your ADU falls or will fall under the RSO, call the LA HCID 

If you wish to get more accurate, then instead of using averages, perform the same analysis against your comps on a per-property basis to determine what the estimated value of the land is on each of the comps.