A lot of people tell me they wish or want to play a bass, and I tell them, if it is in their heart and they want it bad enough, you can do it. I too started out playing piano. I always loved the sound of bass though. I bought my first bass (infamous pink bass of mine) and got home and looked at it and wondered "why did I buy this?? How am I gonna get used to the difference between ivories and strings???" It sat for months next to the piano, until finally I said "heck with it, I am gonna learn this thing" and took it to my computer room, and started learning to play by ear. The first week, I learned a song by ear, and was so proud of myself. I still do not know all the notes on the bass fretboard..just a few here and there. I know the piano, but can't get the bass. But I have well over 40 songs under my belt (all learned by ear), been playing for like a year and 4 months or so, and jammed with two different bands. So you can do it!!

Best of luck!
As far as first basses, I started out with a $70 cheap p-bass. Then started going bass crazy and buying like a loca woman!! Best bet would be going for a decent second hand Fender...a small sized practice combo amp should get you going. I used a Fender Rumbler 20 for a good while before getting a bigger rig. (DO NOT GET A FIRST ACT...I DID AND IT SUCKED AND IT IS EATING DUST NOW)
I love all genres of music, but I found country music easiest...and the slower ones to start with...