1. Does the 3DR oem gimbal housing fit the Hero 6?
Welcome to the drone forum but hey, this was two questions in one.. talk about trying to get value for money... anyway where the heck was I... oh yeah. No, the 3DR OEM Gimbal does not fit the Hero 6 or Hero 5. The sizes, dimensions and interface on the gimbal means there's no way to fit one in. The Gimbal accommodates the Hero 3 and Hero 4.
Or you can modify it a bit to fit?
Well you could always get some duct tape, glue and string and stick another camera in there.... I mean.. you can actually modify anything... put a brick in there if you want... however would it work and give you the same control as using the proper camera? in word "No". It's an unfortunate situation but it's how it goes.
2. Are the cables from the drone and gimbal able to connect to the Hero 6 for full control with the remote controller or smartphone?
No. You could take the gimbal out, put in the stock holder (which is just a basic gopro attachment holder) and stick the GP6 on there. The only thing you'd get though is video feed, you'd have no other control over the camera whatsoever. The stabilization works well enough on the GP6 however as soon as you move from side to side you'll see some crazy tilting action. Technically if you set the angle right and only fly in straight lines backwards and forwards, you can still use the GP6 for some basic camera action. However you also lose the ability to do smart shots. If you want full control of your camera and to experience the awesome things the Solo can do, you'll need a GP Hero 4 black. Trust me, it's a worthy investment.
3. Gimbal (unrelated to Hero 6) : Is it remote controllable to rotate and tilt at will from the drone remote controller or smartphone?
Rotate, no. The gimbal faces forwards at all times, the drone is rotated for movement, However the tilt option is controllable from the controller. You can also program presets into the controller such as maximum/minimum tilt and the amount of time it takes to switch between the two of them.
4. Lastly, where is a good site for me to learn more about the Solo before I go out and fly?
Actually this site/forum right here is pretty good for tips and tricks. Also check out "The Basic Pilot" on you tube, he's got some instructional video's up there. Also read the manual! It's got some good advice and is worth the read (such as how to shut down the motors in an emergency).
5. Oh, do I need to get a license before I fly? Is it free? Or I need to take classes?
You need to register your drone before you fly, that's $5. If you want to sell any of your footage or use it for commercial purposes, you'll need a Part 107 commercial license, that involves taking a test and shelling out $150 and that's good for 2 years. Classes? That's up to you, but a lot of people here tend to buy a cheapo $30 foam drone fly those about and get used to how a drone handles. Those drones are cheap, lightweight, get blown about by the wind a lot and have no GPS. If you can fly one of those and get good at it, then you'll be able to handle the 3DR solo at it's very worst (windy day and lost GPS). The only difference being that when a foam drone falls out of the sky, it bounces off the ground and is ready to fly. If the solo falls out of the sky, it smashes on the ground, can do a lot of damage and take someone's eyeball out.
All in all, have fun flying, enjoy it, but also fly responsibly, obey the laws, and learn what you can and cannot do. Remember, ignorance is not an excuse!
Post pictures and video's of your flights here and any questions you have, feel free to ask!