I’m going to follow this thread, because I’m interested in tips and suggestions as well.
I was actually going to use PicoCMS, but unfortunately some HTML5 tags are not yet supported by the Nextcloud app (PicoCMS itself supports them):
Furthermore I struggled to successfully install themes. My attempts so far always resulted in broken CSS and non-functioning navigation (3 themes that I tried).
With simple and standard pages (didn’t try sub pages so far) it works fine however.