An HOA is a widely used form of community popularized by the developer.  

Market OverviewThe Los Angeles apartment market is comprised of 864,197 units in thirty-seven geographic concentrations ranging in size from the 62,684 unit Hollywood/Silver Lake submarket to the Tujunga/La Crescenta/Montrose submarket, which amounts to 5,448 units.

I would not trust an average number.This will be very specific to your management, your lease, your leased property, the area etc.Some people have made money, but I've not heard much about arbitrage lately, and some have lost money and  not honored their lease.In general this is just a job and not an investment, so it's widely discouraged in this forum.

Depending on the # of licenses, Costar might range from $300-$450/month per user.  

Depending on what percentage of your excess income you put towards additional principal payments, the difference can range from a small amount to a significantly large amount but keeping the mortgage will never pay less interest nor will you ever have access to more funds. 

In Syracuse, the $800k+ price range is experiencing slightly less competition- I had a large complex just close at a 7-cap.

We are a closed group, not open for anyone wanting to join...Some math is pretty universal though - Let's take a home in your "sweet spot" range - ARV of 700k.

Here are the other choices in this range: https://www.zillow.com/homedetails/162-Ash-St-Santa-Rosa-Bea...https://www.zillow.com/homedetails/49-Debbie-Ln-Santa-Rosa-B...https://www.zillow.com/homedetails/70-Pointe-Cir-Santa-Rosa-...https://www.zillow.com/homedetails/429-Montigo-Ave-Santa-Rosa-Beach-FL-32459/67187461_zpid/?

That mid-range investor if doing a fund in that range is going to be very difficult to find enough product, cover your overhead and pay the investors. 

I could move that equity into other projects, including properties that would rent for more efficient rates (rentals in the 3/2 to 4/2 2000sf range here tend to go for about $2200-2400/mo).