"we'd have a "standard" set of modules, which would either be completely replaced or slightly modified as necessary to fit the client company"

This is what a dozen of my customers have suggested. (You know you're on the right track when your customers are pushing you into a business.) I'm doing something like this but with a few twists.

Thanks for the side note. I have start-up fever and am married to my project. But I'd love to stay in touch.