Complte working examples of (1) cross document table updating automaticaly and (2) custom widgets

(1) I am making a grist workspace with different documents inside. In one documnet, I have tables like general ledger, people, projects, which I want to refer to in other documents. I’ve read that cross document referencing ist not yet possible and it is suggested to copy these reference tables to every other document that wants to reference them. Manually copying is error prone, since these tables will be updated as new transactions, people or projects come.

So, I am seeking a complete working example of how to do this automatically, with all the code and the necessary steps listed and explained (e.g. where to place the code, where/how it is invoked/started, etc).

(2) Secondly, I would like to have a form/dialog/page, where I can input some (e.g. configuration) data into fields that arent related to any table, save them permanently, or based on that to invoke an action. I learned that this is possible by using custom wigets. There some partial examples.
Where can I find a complete working example?