What are the biggest challenges people have faced with this. Also how do I make sure to get good tenants?

Since you're looking to expand into Florida and other states, I'd recommend starting by narrowing down your focus:Market Research – Florida has great opportunities, but each state and city has different laws, taxes, and demand drivers.

Where can I find the info on how you group the different neighborhoods into classes? 

That's looking at it through a narrow lens though, when you zoom out to 5-10-15 years down the road and calculate the difference, in my experience the appreciation has been far more beneficial than the $200 difference per month in cash flow from a different market.

Every state has a slightly different process, and time frame for each step, so you may want to consult a Realtor for your state process.

The growth in Chatt (in part driven by it appearing in every single "best place to retire" vlog from 2010 onward), is in a different league.

If not you might want to seek a different agent.

How long it takes to be financially ready is different for everyone.

ABL, which is the basis for HML/fix and flip lending, will have different criteria and different focuses than multi-year loans based on cashflow and borrower credit score (long term mortgages).

There are Different ways of structuring lease options.