Sounds like a good idea, I'll check it out! OctaMED doesn't need a MIDI keyboard, but it can use one if you have it. It's perfectly possible to use the normal keyboard instead when you're building up your tracks.
An alternative to DPaint that you might look at is PersonalPaint
, which is similar but supports many different formats and has an ARexx interface for loading plugins. Version 7.1 was released free years ago, version 7.3 is currently supported and still being developed and sold. I still use it to this day for doing some web graphics and the odd bit of icon drawing or what not - I find the flexibility and straightforward operation a refreshing change from Fireworks for example.
is a very good music sequencer with MIDI support, and supports more modern hardware and techniques than OctaMED. Definitely worth a look!