I am personally doing all that with my own Sciter Notes [1]. That is a free form personal database of HTML documents if you wish.

With notebooks, tags and events.

For customers I have single template in form of definition list (html's <dl> under the hood):

  - principal contact:
  - address: 
  - service until:

So to make new customer I simply copy that template and fill those fields. Adding more info if needed for particular customer, etc.

[1] https://notes.sciter.com GitHub: https://github.com/c-smile/sciter-sdk/tree/master/notes