Werner,
I assume that you mean "using Form Builder and Form Runner".
1. Form Builder has an Edit Source button, where you can see the form's source. It's disabled on demo.orbeon.com for security purposes, but if you download the WAR and install locally you will have that feature.
2. See "section templates", which can be created from the builder:
https://github.com/orbeon/orbeon-forms/wiki/Form-Builder:-Section-TemplatesThere are also other types of components, see:
http://wiki.orbeon.com/forms/doc/developer-guide/xbl-components-guide3. What you mean by "own XForms"?
Regards,
-Erik