I would agree with "swimmersonboard" that, especially for your first cruise, you book shore excursions through the cruise line. If you are not familiar with the ports, the excursion will be a safe way to explore, and even if you are, then if something happens that delays your return to the ship, they will wait for you. If you are on your own, or with an excursion not booked through the ship, they won't wait for you if you get back late.
I don't remember a ping-pong tournament either, but that doesn't mean they don't happen. You can certainly ask - check with the cruise director's staff after you are onboard.
Whether you will enjoy an inside cabin is really a matter of preference. For your first cruise, they're a nice inexpensive way to be introduced to cruising. There will be a TV in your cabin and one channel will show occasional pictures taken from the bridge, so you'll be able to check out the weather.
Inside cabins have the advantage of being nice & dark at all times, making those afternoon naps, or sleeping in, a bit easier. (Bring a small nightlight, though - you can plug it in the bathroom or the main part of the cabin so you aren't stumbling around in the dark if/when you get up at night!
) Most cabins have beds that can be made either as twins or as doubles/queens. You can request ahead of time which configuration you want the beds to be, but if you don't get to do that, you can ask your cabin steward to change it. If you don't see him or her before dinnertime that first night, leave a note in a conspicuous place (like on the middle of a bed) requesting what you want.
Best advice: relax and have fun!! Don't sweat the small stuff, as there are usually some small glitches. Have a fantastic cruise!