What is best practice for creating records in 1Password?

I don't know if there is an official best practice, but I made these rules for myself:

• if there is a website login or app login I want 1Password to autofill associated with the record I want to create, I create a "login" category entry.
• otherwise, I create a category whose fields matches most closely the fields I intend to enter.
• after creation, I add custom fields for every information not present in the category template used.
• Border case: software license. If I need to save registration keys and purchase information and at the same time the purchased app requires some internal login, I might create 2 entries, one for the login and one for the license if the app requires me to enter login credentials every time I start it, but only one software license entry with custom username+password fields if I enter the credentials once at app installation and then never again.

If it happens there is category for the entry, but there is also an associated website login, I create a login entry and add the fields as custom fields. And no entry with the specialized category. It's possible (and probably designed by 1Password) to link multiple entries, for example a specialized category and a login entry, but I found that cumbersome and not user friendly. I rather have a single entry with everything in it, and no linked entries. Linked entries clutter my vault, and I tend to always open the wrong entry.

So, in your case of a gym membership, I would create a login entry, because there is a website login. I add the additional fields like address, phone numbers as custom fields to the login entry. But this is only my personal preference. For categorization, I would add the tag to this entry that collects all my family/real life (non computer) related entries.