Get sample CDs for making mods.Also , if you plan to compose some very
advanced stuff you should also know notes (well not those ugly real ones ,
rather their alphabet counterparts C1 (do , low octave) C1is , D , Dis etc.
Learn hot to compose simple drums , that's easy , most mods have very nice drums (some even bass lines but not a must).
More than anything get some normal software to learn how to compose music you like and start from there.Once you recorded your song on synth it will be
pretty easy to make a mod file if you have good samples.Keep in mind that
four channel limitation (four samples at the same time).
I only play Guitar and Base Guitar but had no problem with any tracker and I know very little notes.Oh yeah , watch how mods you like are made to get a better picture (and steal a few tricks :-) ).
Most guys I know who played Piano (synths) used keyboard to input tones
in trackers once their songs were done.You can even use Amiga keyboard
as "secondary" synth

.
Looking forward to your future work

If you need bass/drum lines and are willing to give me samples I would be
glad to help.