awsome idea of be able to customise and show/hide what we like!
I also agree in keep showing the grayed buttons. This comes in hand with the commend I made in the search bar improvement a lot of time is a simple issue of data type that does not allow us to use a specific filter. furthemore, it is a great way to discover new tools inside paraview.
for 5., if implemented it should be also possible to turn off, for a UI/UX perspective dropdown menu can be quite annoying for a lot of users. the i went from 1 click to 2 clicks, this has been prompt so many times in freeCAD UI/UX redesign.
agree also with @theodorebaltis in the reset/zoom to data/ etc, i simply click it randomly till i get what i am looking for. it is dumb from my part? yes, but when i tried to remember after a few days of not constantly working on it i forget.
and also agree with @Yann on the open/save data, I sepecially do the File> because i have already overwrithen a saved stated by trying to load it but hit the save by error.