I've just embarked on this journey myself. I have a long background in music and play the sax and (tried to play) piano.
Pat's right - software-wise try everything! I started with Octamed SS but wanted to add live instruments so I needed a recorder. Then I noticed certain sequences were better done in OSS (the volume, effects, and duration could be edited) but sometimes I want to play along with the other parts so I use MIDIIn and AHIRecord. I also got a MIDI serial interface, MIDI KB and a mic and mic preamp. Once I have a few parts recorded they're mixed with HDRec.
Rhythm is pretty instinctive but for chords and harmony study the Circle of Fifths.
My Amiga is very high-spec for a classic so I'm not sure how much of this you can do. Even with the 040/40 the mixing to HD doesn't happen in real-time. Since the machine has a SoundBlaster and native audio I can effectively record Octamed as if it were a live musical instrument. Since the recording and mixing are done on HDD a fast IDE/SCSI interface is recommended. I "get by" with the built-in IDE but only because of the buffer and the quicker CPU.
Hope you have fun! Enjoy!
