Little add:
It is also stated in the iodéOS part of their FAQ about microG .
So not specifically about Apps in general, but specifically to my question about microG. 
Also it seems to be possible to already skip/uninstall during setup. (“… you can also uninstall … directly from the setup wizard…” ). When I have some time I will flash iodeOS and go that way.
Edit (already installed it):
When your boot into iodeOS the first time you have the choice and can select what Apps you would like to have. For those you de-select the state is “Hidden, data deleted, uninstalled on next reboot” as you can see.
They can all be reinstalled (as discussed in the other Thread) and you have to reboot again before they show up (Status after hitting “Install”-Button → “Installed on next reboot”).