I now reorganized my Xwiki as suggested (and also re-inforced here) and created a new start node.
Previously, I tried to replace the start page’s contents, but it somehow was reset to the default contents with a subsequent update - is it possible that this happened and to be expected, or was this probably caused by a mistake / mess-up on my part?
Anyway, I thought I’d easily create an alternative start node / page and configure this to be the Wiki’s new “start page” - until I discovered just now that this is not really possible due to an open bug / unimplemented feature.
So if you just access the Wiki server URL in the browser, you’ll always end up on the default home page. 
I can replace the default start page’s (“Main”) contents with a redirect, but will it be overwritten by subsequent Xwiki upgrade (see question above)?
Alternatively, I could configure a redirect on web server level (I’m hiding Xwiki behind an Apache reverse proxy).
However, I’d like the redirect to redirect to the configured default Wiki start page, not explicitly to a specific page - i.e. if possible I do not want to have to remember to adjust the redirect whenever I reconfigure the default start page in the Wiki descriptor again. Is there any URL which will automatically redirect to the currently configured default start page and which I could use as a redirection target URL?