decent mics cost over $150 don't bother with anything less than that, trust me.
Midi keyboards are so outdated. You can plug any electric piano, keyboard, or whatever into your computer using your sound card, goto radio shack and they will tell you what cables you need.
Aside form that, the good software, Acid, Magix, Garage Band, they are all expensive if you want the good features. As a hobby, frooty loops or whatever it is called should work fine, but is very limited.
Still keep it up, even as a hobby it is always cool to be able to show off a song you made to your friends. Especially if it is a good song people can dance to.