as far as windows 10 to windows 11 upgrade is concerned, it is likely to be offered as a free upgrade through windows update, if the device meets the minimum published spec at the time.
the upgrade should not affect installed apps, you will be notified at the time if you have any apps that are not compatible.
it is always wise to perform a backup prior to the upgrade in case things go wrong.
we will get more information nearer to the launch, with a poor or limited internet connection i would not recommend joining the insider program.
for your Microsoft Office question you would be better of starting your own thread in the Office forum, the experts there may have some advice for you.