How do you mean heavy? Weight wise? They’re only a few pounds, I sold one last year. TBH it was a little on the light side for an insturment with pads, that’s part of what I prefer about the 2000xl (and the 2000 and 3000 had even more bulk to them).
I had a very similar setup for a while, with the Octatrack mounted on the MFC-42 mounting kit. Worked well but it’s more practical for me to keep them arther apart, since I use them for different things. The MPC is near the master keyboard and is what I use for all my sequencing and routing the master keyboard to different channels more conveniently than changing its own channel setting. The Octatrack is the master clock and I have it sitting at the other end of the room on a little stand with a preamp and use it for live sampling and looping the things that AREN’T sequenced. The MIDIbox SEQ v4 I built a couple years ago does all the step sequencing.
If I start playing out again I’ll probably use the Octatrack’s sequencer with one or two little desktop synths and leave everything else home.