You can train for three years in internal medicine. if you get a 'fellowship' (aka subspecialty), you would apply for another Statement of Need. You would continue to train without a break.
the home country presence requirement does not stop you from working/training in the US for the fellowship using the J-1 Visa. The thing to remember is that the two year home country presence requirement prohibits you from applying for an H1B visa or green card right after training.
The 'waiver' of the home county presence requirement is just one way the US cancels the 2 year requirement.
Thing is, if you really prefer to practice medicine in the US (Alaska), then IMHO you should not bother with the J1 visa, you should get the H1B visa. You get six years maximum with the H1B, and then you can apply for jobs in the US where ever you want without being limited to under-served locations in the US.
If you use the J-1, and decide to work in the US, you have to finalize your waiver job before you finish your training. Once you're done training, you can't apply for a waiver job, you have to go home for two years.
But don't take my word for it. The EVSP (ECFMG) will explain the rules of the J-1 in detail. There are hundreds of lawyers in the US who would be only too happy to take your money to explain the ways and means of waiver jobs.