Use the frontend menu GUI to create admin menus.... for each roles.
Absolutely. Even better, provide a front-controller for the admin (like the front-end uses) so that we can use clean URLs and more easily hack admin URLs for faster power-user navigation.
We need a better admin dashboard, definitely.
However I don't think re-using the front-end menu GUI is the right way to go with this.
Other than that specific detail, I think this could be a duplicate petition of https://petitions.classicpress.net/posts/102/implement-clean-urls-in-the-admin.
I'm going to leave some more thoughts over there.