Is it correct, that this template does not provide any editor ‘package’ at all?
I’m just wondering, if this is expected - and - I have to add for example ‘vim-minimal’ myself - or - if there’s a specific issue with my installation / setup …
Yes, AFAIK this is expected. It is implied in
<Minimal templates | Qubes OS> that an editor like
Vim is not pre-installed for Qubes OS's minimal templates (See
"Distro-specific notes").