So, all in all my upgrading the desktop computer from Debian Jessie to Stretch https://www.debian.org/News/2017/20170617 was painless as expected and I could have skipped the process of ensuring that I had recent backups of the important files :-)

Thanks and Kudos to everyone who was involved in making this possible! <3 https://social.diekershoff.de/photos/tobias/image/c1a50a6d73d7955465325da90ca3f2c6