You also want to make sure it has at least 88-keys, the more the better. If you plan to play classical, there's nothing worse than running out of keys...
As for sticking with it... I've been playing for more than 20 years. There was a time that I stopped, around the age of 16-18. I had other distractions, but I'm definitely glad I went back to it. Nothing more relaxing after a long hard day at work than to play/make music. Just remember to practice, and you'll get better over time. Don't give up too easily...
As for purchasing advice... well...it's all about how much you want to spend. In the Navy, I bought a cheap Casio that had 88-keys, light enough to carry around and stash. One thing I remember about it, it sounded and felt horrible, but it was something to keep on practicing. When you start getting better, you'll soon realize that it needs to sound like a piano so you'll soon upgrade to something better, and prices go up pretty fast. I've gone through 5 or 6 keyboards through the years. My dream is a baby-grand, but hehehe think about moving that around. I'm pretty happy now with a Roland RD-700 with the Concert Piano sound upgrade.
Oh...and another thing...try to take a few lessons. I've seen people try to teach themselves, and i think it just doesn't work.