I'd stay away from duplexes and concentrate on 3 and 4-plexes where you can get better efficiencies of scale.

In a reversion people may down grade to lower cost units and the Class A stuff might take a hit because they will have to lower rents to compete.If you have cash, you may be able to get properties at a significant discount from owners that bought poorly or over paid during the sellers market.Generally speaking the default rate for multifamily remained low during the 2008 crisis, most of the losses were concentrated in a few markets (Phoenix and Miami come to mind).

As investors we aim to make 10-12% net per year from a deal, where is the best area to concentrate on?

I have come to terms with looking out of city/state but get overwhelmed with trying to narrow down a city to concentrate my efforts.  

You will likely make more money that way and have more time to concentrate on your medical practice.You can find them by looking at similar properties for sale or lease on Loopnet or CREXI in your area and talking to commercial brokers in the area.

Often times loan officers and owners confuse overall investor concentration vs individual investor concentration. 

So I guess my ultimate question is should I concentrate solely on raising my credit score and getting back in the good graces BEFORE I start looking for deals?

As the White Coat Investor urges, if you live like a resident for several years after you become an attending you will be able to get rid of the albatross of the loans faster, then concentrate on your real estate portfolio.

There might not be a more concentrated source of DM wisdom anywhere on the internet.

If you are not both in this 100% I would advise against going forward and simply concentrate on finding yourself a job with a future and get off the pay check to pay check life style.