Pages or posts for reference site
There are 2 things here:
1.SEO:
There is absolutely no issue in terms of ranking when it comes WP pages vs post. As long as you got rich content either should be fine.
2.Website Structure:
Pages vs Post could come under your website planning and future consideration. For general understanding, pages are generally for website page and posts are for the blog.
Note: Also, it's good to have fewer pages with rich and good length content instead of having 100s of small pages.
Before I get too far down the rabbit hole should I make this kind of content as pages?
Doesn't really matter as long as you remain consistent with it. Personally, I would make this content into a custom post type and that would allow for custom taxonomies to better handle navigation and SEO issues, but this isn't necessary.
The fear is that eventually I could have hundreds of these pages, is that a problem?
Nah. Again, as long as you are consistent about which content container you use, there's no benefit nor penalty to using posts over pages.