Just a heads up but if you can stay in the Marines on active duty then you might want to consider that especially if you're looking to try and come into the Army on active duty.
The Army isn't really taking prior service on the active side and with you being an NCO its going to be even harder unless you have one of the very few critical MOS's that they need.
As for the duty station and the 68 medical field both are very hard to get even for first time enlistees and again pretty much a no-go for prior service unless you're interested in the reserves and then you might have a chance for the 68 medical field.
The Army is making it almost impossible for prior service to enlist on active duty and since they lowered the enlistment age from 42 down to 35 if an applicant doesn't have enough time in service as a prior service, any hopes or dreams one might've had of re-enlisting are pretty much a wrap.
I myself am prior service Marine and wanted to go active but had to enlist in the reserves just to get in this past April with the intentions of going active after I complete my AIT which I leave for in July. I spoke to a few people at my reserve unit and was told that they are really good about releasing soldiers to active but if there's no prior service slot available on the active side then its just a waiting game at that point.
Good luck and thanks for considering our Army....