Thanks for the feedback!

1) The tag from the web container has to be sent to the endpoint domain of your GTM server-side container. You can then add a path (e.g. /event), which you can declare in the config of the SSGTM client.

You can change the collection domain and the path in the config of your client-side GTM tags (where and how will depend on which tag / requests you use).

2) Yes of course. You can use the custom client execution as a trigger for the SS GTM tag that fires the tag server-side.