No, your design is good, as long as the notes can be different in Seq1 and Seq2, that's great. Triggering both always together is even better.
Having a few more "shift" buttons would be interesting for future extensions, I was thinking of 5 buttons, one center button, around it four arrow buttons in each direction: up, down, right, left. Then you could use those, in all kind of combinations to access even more (future) functionality, e.g. various pattern saving/loading/changing functionality.