Yeah, I remember back when I was a senior, and pretty much flying by the seat my pants. I wasn't like you and thinking about the future, asking good questions of people I respected. You sound like a level headed guy!  
That's good!

my 2cents:
Don't do things because of an expectation. If you're doing it to become famous, rich, or important,, then you might get it, but then you've started a never ending trap where you're always trying to achieve something and never allowing time for the enjoyment.
Most of these guys said "go with your heart", and that's the best advice.
Do what feels right, and resonates your soul.
You can't go wrong.
Maybe drumming won't end up being part of it, maybe it will, but your heart won't lie.

At your age, you have time.  Go for it if you really want to.  Work as hard as you can at it, give it all you've got.  At this point, you have little to lose.

If it looks like you're not going to really make it (this happens to most), you'll need some other way to make a living.  So, keep doing the things that will make that a good deal.  A serious effort to get ready for most other jobs will have a much better payoff in the cash department.

You'll probably end up being a weekend warrior with a day job and the wife and kids, etc.  But, while you're young, take your shot.  There's always an offchance that you'll make it.

I'm 17 years old; what is expected of me as a drummer in a pro band? What equipment do I need, what type of music do I need to know, which songs do I need to know, etc...? Can I still play at bars and night clubs if I'm a minor?

What's the best way to gig often? Stick with a certain band, sit-in for other drummers, etc...?

I want to gig, bad. I guess I don't really know where to start.

It depends on what's happening musically in your area. At your age I was working most weekends in a wedding band, I was playing in the orchestra pit for theatrical productions, occasionally playing a bar gig, subbing for other pro drummers I'd befriended, etc. I joined the musician's union at 14, if I remember correctly. My band director in high school had his own professional group, and he'd use me occasionally, and he passed my name on to other working pros.

Learn your local scene, and look for your place within it. Pay attention to what songs they play, and learn them. Find out who the working pros are - maybe through the local union, or by checking to see where the local drum teachers can be found gigging. Get to know as many pros (all instruments, not just drummers) as you can. Find out if you can get away with working in clubs. Also, make sure all this is okay with your parents.

If you can't read, learn. Equipment-wise, have a good-sounding basic drumkit, and keep it in good shape. Be able to set it up quickly. Beyond that, you don't have to have any special equipment. Print up business cards with your name and number. You can do this cheap with your own computer, and print them on pre-perforated sheets of card stock you can buy in any office supply store.

To do weddings, conventions, and other corporate work, you'll need a tuxedo or a decent black suit. It's helpful to have a versatile appearance, and to be open-minded about modifying your appearance for specific gigs.

When you play with older musicians, shut up and listen. Follow their directions. Watch them like a hawk while you play. If you can't hear them, play softer.