I think you got it right. I’d still create a test user to ensure everything works as expected.
I would describe “chat allowed groups” as the general setting. You cannot use anything of the chat plugin without being allowed to use chat.
Chat channels are based on categories, so you control access to them with the category security settings. That’s why there is no separate setting for them.
Being able to create DM chats (1:1 or group) is controlled by the direct message enabled groups setting.
All chat settings are independent from the settings about personal messages (those which are like topics, have a title, and appear in your inbox).
The only overlap are the permissions for chat channels and topics. Those are both based on the category’s settings.