Your first statement scares the hell out of me. I have seen too many people repeat exactly that right before they got out of control. I don't know that I believe that just on it's own merit. Comfortable for long rides, not a touring bike, Harley less than $10,000. I've got nothing for that price. Add another $10,000, and don't worry so much about a longer comfortable cruise without getting a touring model, and you have a wide variety to choose from. I would go a Crossbones given the choice.
Once you are an active duty Marine, you will have to tell your chain of command you intend to purchase a motorcycle. After the financial counseling to make sure you can afford it at your pay, you can purchase one with your commands approval. You will have to attend at minimum two training courses before you can get your license. The first is the basic riders course, and the second is the experienced riders course.
If you go the sport bike style route you willhave to attend a third course from the Keith Code school for sports bikes offered in our area every quarter.
At your first regular unit you will be on Force Protection Program which makes you automatically high risk when you have been in the unit for less than one year so your movements wil be pretty limited. You will have to check in with a mentor every day, but should have plenty of people around that ride. You are limited on a regular weekend to no more than 250 miles away from your base, and no more than 450 on a 4 day weekend. If you are part of an east coast unit like Lejeune you will have to fill out a liberty package every weekend that is more than 48 hours detailing a safe liberty plan.