I use both Windows Photo Gallery and Movie Maker on a Win 7 System.  (I believe the latest incarnation of these products is as part of Windows Essentials 2012).

1)  Will both Photo Gallery and Movie Maker continue to run seamlessly after an upgrade to Win 10?   Implicit in that question is this:

2)  Will my Photo Gallery database be preserved and remain consistent with my Media (stored on a NAS) after upgrade to Win 10?

I have added much content (tags etc.) to various media, including video clips, which is stored in the Photo Gallery database, and I don't want to lose that data, and the capacity to search it which Photo Gallery provides.