Finale is a great sheet-music based music composition program. It offers playback with decent sounding virtual instruments. I've heard good things about Sibelius. Both have free versions. Check out this wikipedia list for similar programs.
As far as learning to compose, I would give species counterpoint a try. While it may seem distant from your ultimate musical interests, a basic understanding of counterpoint can clear up a lot of confusion about the cooperation of harmony and melody. Employing any amount of counterpoint will make your music much stronger (frankly, it's far under-appreciated in popular music). I used Norton's Fundamental Counterpoint as an introduction to species counterpoint, and still use it as a reference. Giovanni Dettori's Art of counterpoint series was a good watch, focusing less on the details of strict counterpoint and giving a good overview with a nice little example fugue constructed at the end. A basic understanding of harmony, as can be found all over, will be useful for these studies. One big thing to take away from counterpoint is how to avoid cluttering your music with too many clashing melodies.
Depending on how interested in harmony you are, try the following noodle-tactics (definitely take your time). Mess around with chord progressions on your keyboard. Start with the chords of the diatonic scale. Play chords in the left hand, running melodies (in the diatonic scale) on your right. C major is nicely contained in the white keys. Try focusing on root motion in fourths, seconds, and sixths. For example, play C to F (fourth) to G (second) to Emin(sixth) to Amin (fourth) to Dmin (fourth) to G (fourth) to C (fourth). Motion up a fourth is especially powerful. Try adding in extra notes from your scale to your triads. When you play the dominant chord of a scale, try throwing in the subdominant note, making a dominant seventh chord. As a way to become familiar with all keys, move down the circle of fiths by moving up perfect fourths, playing the major chord of each. So, Cmaj to Fmaj to Bbmaj to Ebmaj, etc. Experiment with making some of them dominant seventh chords, and some of them minor chords. Focus on the sound of each device.
Try just messing with single line melody (diatonic at first, slowly trying out accidentals). It may seem really boring at first, but getting an ear for how melody works without accompaniment makes your melodies more robust for adaptation to your various harmonies.
Get a feel for how rhythm affects all these things. Syncopation is fun.
Afraid I don't know much on how to best use the electronics! The sound of an instrument affects a lot though. Try not to over-complicate your sound with too much chorus-like effects and distortion.
When it comes to composing and being creative (which you always occasionally be doing), use the cool stuff you've experimented with, but check in with your heart every so often. Try composing to some simple forms. Make a chorus and a verse and put them together. Or don't think of them as choruses and verses and experiment combining pieces into bigger objects in general. Even simple melodies are made of pieces. Consciously mess with structure and get a feel for overall flow. Every so often, stop and just listen to what you've got with a clear head.
Play to your dog. If you're outside, play to the trees. When you play for your crush, keep it simple, stupid, and make up some gushy lyrics.
