Can't really comment on what would be the 'best' approach, but once the apps are installed in all profiles, no matter what case u used, updating 1 app in 1 profile will update the app across all profiles containing that app as far as i'm aware.
Not sure about droid-ify, but u might have issues installing f-droid in all separate profiles as they host an older version on their website and then update while installed. When u want to then install f-droid in your second profile, the versoin u will download again from their website will be older as the one already on your device and won't let u install.
Edit: ultimatly u choose what u do with your device, but f-droid isn't really recommended from a security perspective, as is ironfox or any gecko-based browser because of lack of sandboxing in android. (Although ironfox made a nice step, from a security perspective its still not even close to chromium based browsers).