Hey Devon,
Well i guess the biggest difference for you will be the computer working out all your inbetweens for you automatically rather than having to do it all yourself frame-by-frame as you have been doing in stop motion. It's like a shift from the persistence of vision stuff you will have been relying on to the arcs and curves of the animation that become so much more fiddly (and rewarding...eventually!) in 3D. I think in terms of habits etc it really depends on the style you animate in right now - if you are a straight ahead kind of guy then you can operate in much the same way in maya, whereas if you tend to plan your key poses and then go to fill in the tweens after then it would help to get to know the basics of the graph editor first to scrub through (stepped keyframes rather than curves etc, nothing too tricky). The best thing is to dive in and start practising really! 3D can be frustrating when technical errors stand in between you and what you want to be happening in the scene, but the internet is full of tutorials and fixes, after a while it almost becomes half the fun really haha.
Good luck!
Tom