Keyboard is definitely an awesome way to go. I salute you for that! I might invest some money in a music theory book (any will do really) and figure out some chord structure. From there just play around on said keyboard. Hear the chord, get it in your head. That's a fantastic way to start training your inner ear to hear anything you want to compose. The biggest deal is learning all the notes then fooling around, you'll eventually teach yourself some basic piano. Your technique might not be perfect, but unless you intend to get serious with piano, that all you'll need.
Hope I've helped...
