Design Q: Lots of little installs or one giant one?

Hey there. I’ve been exploring Jekyll lately and need some implementation/architecture advice.

I’ve been maintaining the same site for over 20 years now, and it has accumulated thousands of pages of content, stretched across many disparate sections (all with their own visual design, URL design, etc., etc.). Some are CMS-controlled. Some are wiki-controlled. Some are plain HTML. Some are just “files in a directory”, etc… Some sections are updated frequently; other sections haven’t been updated for over a decade. Only one of them is “like” a blog. Ideally, I’d be looking to convert all of this into a Jekyll-based implementation, but I’ve seen various laments about how “slow” Jekyll can get over time. I’m only “barely” interested in “slowness” discussions; given proper CI/CD, I don’t much care if the resultant deploy takes 10 minutes or more.

What I’m more interested in is whether I should do ONE INSTALL (one git repo) for many disparate sites/sections/mentalities or whether it makes more sense to do MANY INSTALLS, one for each particular “section” of the site. I’m mainly worried about overhead, I guess: “many unused layouts” (i.e., unique looks for each sections) or “many variables” (i.e., “I need 23 variables to build this section, 17 to build that section, 0 for this section, and none of them are reused for other sections”), or any other concerns (“with 17 different installs for 17 different sections, you’ll be unable to make a single top-level index.html that represents a latest-update news feed”, etc.).