Three primitives you want to have in your admin app, for accounts: arbitrary text notes, arbitrary tags, and an activity stream. Just build them. Your CS, marketing, and sales departments will thank you later.
If you want to go the extra mile, a programmatic way to tag accounts and a non-programmer-friendly way to mass tag accounts (via e.g. uploading a CSV and matching against their email address) will make people very happy with you.
Also a way to trivially (i.e. without bugging anyone in engineering) download a CSV of as much data as you can reasonably summarize with regards to anyone having a particular user-defined tag.
People will find *surprising* ways to combine these primitives if you make them easily available, and they will do amazing work with them. (e.g. "Hey guys I figured out how to do analysis of LTV by cohort in Excel." "Wait we don't expose... oh.")
(Why do you want a programmatic way to tag accounts? Because you're eventually going to do something like have a bizdev deal with FooCorp with /lp/foo as a landing page and wouldn't it be great to tag them as from-foocorp for ROI analysis? Yes, it would be, and that is trivial.)
