I am concerned that there might be an event where the loans are called and it being difficult to find other financing.

Depending on the market it may be difficult to find a deal so getting a deal off market with no competition is a plus.

Are there restrictions and limitations above 6-beds that have a more difficult barrier to entry?

If a lender is familiar with an area; they are more likley to feel comfortable lending to a new investor since it probably would not be that difficult to finish the project themselves and sell.

You can be successful in any class, albeit some are more/less difficult to succeed in than others.

I'm guessing evictions are difficult to do in that market, so you'd want to avoid them if possible. 

It's unbelievably difficult to get an understanding of what all the current laws and regulations are regarding moving in to an occupied unit.

It has been incredibly difficult finding individuals willing to work. 

Getting a contractor to wait to get paid until FHA inspects the completed work and releases the rehab funds is more difficult than you may think. 

Pay close attention to items that will make your project difficult, waterways, water courses, ditches, canals etc these are either easy obstacles or deal killers.4.