So I’m not sure if this is doable, but I figured I’d ask.
I want to use WP as the backbone, but have the interface look like a directory with categories & then relevant products/services under those categories.
I know WP sort of looks like that already, but it doesn’t look or act like a full blown directory.
Yes, pretty much anything can be configured to run over the top of the WordPress engine - especially where there’s a taxonomy or categorical structure required. What you are asking for would probably need some custom themeing and a variety of plugins to get what you are after. If you provided an example website we could probably give you an idea of what was specifically required.
WordPress is supremely capable of doing this type of functionality. The categorization is the key - it’s just a matter of shaping the data you want to add (the posts) to those categories.
There are plugins that can assist, but it’s not too hard to custom-code: