Something worth considering is to go with the Expert Sleepers FH-2 and turning the Disting mk4 into a Disting EX. Getting the FH-2 is simply to make space for the EX. The FH-2 may not be what you want in this case in which case this would be moot but it seems like they would have the same purpose for this system. The EX is basically the same as the mk4 but it is 100x easier to use. If the FH-2 works for you, I would do this. You also get the benefit of having two mk4s in one.
In regards to a pitch sequencer, which I do agree that you should probably look at, it depends on what you'd want. If you have something like an MPC One you can pretty easily use that. Same with a midi keyboard. A common one that is used with modular systems are the Arturia Keysteps. The Digitalis is a good small option.