1. There's a lively discussion on the topic of what to do with your weapon while driving:
This is the "short" version:
2. OC is legal in restaurants and bars, owner or manager can give notice at any time and you must leave if asked. That applies to all private property, of course. Alcohol consumption while armed is legal up to .08 (also legal limit for driving). At .08 it becomes a felony weapon violation.
It is unlawful to have a loaded firearm or crossbow in or on a motor
vehicle (including trailer, ATV, aircraft, snowmobile, or railway car). A loaded clip may be carried in a
motor vehicle, but it must not be inserted in a firearm. Persons who hold a Maine concealed firearms permit
may carry a loaded pistol or revolver in a motor vehicle. Firearms may be transported in a motor vehicle
without a concealed firearms permit provided they are (1) unloaded and in plain view, or (2) are
unloaded and placed in a remote secure area (such as a locked trunk) away from the control of the
occupants of the motor vehicle. For purposes of this law, a muzzle-loading firearm is considered to be
loaded only if charged with powder, lead and a primed ignition device or mechanism.
Personally I never drink if I'm carrying open or concealed but to each his own.
3. Public property is unregulated (generally speaking). Check out http://maineopencarry.org/law.html for examples of no-carry areas. That list isn't all-inclusive though.
4. OC is legal without a permit so no real particular regulations unless you plan on going to Acadia National Park (OC prohibited, CC legal with permit) As long as the weapon stays holstered and there's no action that could be construed as brandishing or displaying intent you should be fine.
5. Maine Resident and Non-Resident confer the same legal protections, to my knowledge. Might want to send Paul Mattson a message at http://www.mainecwptraining.com/Contact_Us.html or ask a lawyer to be really sure.
Maine is more OC friendly than it used to be. You will probably get mixed responses in Portland, Augusta, Bangor. We've been visible enough that LEO seem to have gotten the message that Man OC'ing Gun is not doing anything wrong.
Maine has castle doctrine and the place you pay rent is legally your domicile so lethal force is authorized if someone is conducting a break-in. You legally have the right to assume a home invader has malicious intent and capability if they are breaking in while you are inside.
Non resident permits go through State Police, you can get the application here if you don't have it already:
Some med release forms (psych background), background questionnaire. They will run NALAC but you should have no issues since you already hold a valid CCW in another state. State PD legally have 60 days to either grant CCW or deny for cause. We're "shall issue" for resident, not sure for non-resident.
DD-214 with Honorable discharge exempts you from the "demonstrate knowledge of handgun safety" requirements you'll see on the application.
Others may have more to contribute, feel free to email me if you have other questions as well.
Also, forgot to add, Maine has state pre-emption so you don't have to worry about moving between municipalities and inadvertently becoming a criminal: