Hi Emily,
Item #3 of your wish list is finally coded:
https://neuroimage.usc.edu/brainstorm/Tutorials/MontageEditor#Custom_montage
https://github.com/brainstorm-tools/brainstorm3/commit/d0b5a90a52db31f6ac8ef90d521eca1d206ac4c6
We can keep on working on the other points.
Please keep us posted with all your great ideas!
Cheers
Francois