as far as cost that depends on too many factors to cover! 

Neighborhoods to invest in is a more subjective topic as that is often dependent on the type of investment you're interested in, your price point and even the type of tenants, if that's the route your going,  that you are trying to attract.

Depends on the city & airport. 

Each program is a little different so it just depends on your situation and income.They are quick and easy though once you get your certificate you can work with any Bank or Lender that is approved to use those DPA's.

Section-8 rentals are great because of that dependable income.

As others have mentioned, DSCR loans are generally for turnkey rentals (although outdated rentals may still qualify depending on the level of deferred maintenance). 

It depends what your goal is.

Quote from @Paul Lucenti: It depends what you're looking for.

Both Conventional loans and DSCR loans can offer this flexibility, depending on the specific scenario and borrower qualifications.

This will all depend on how good of negotiator you are.