@knuthollund That should be smooth sailing (unless, like me, you've got homegrown scripts which do some maintenance work and suddenly PID files go missing because of systemd-ifcation). But Debian is awesome. It'll work out fine for you.
One thing with Apache (because I think you'll go from 2.x to 2.4) is that they have new syntax for access lists. The htaccess.sample in !gnusocial has a section with an if-statement which provides both syntaxes for each version. Could be good to look at if you wonder why #Apache won't start after upgrading :D