I've attached your template.
For item 2 - sometimes when we change the schema in a form that has complex XPath expressions like this, the "current()" function is removed - so you may want to get your schema design wrapped up and then add these expressions
For item 3 - when controls are added, fields are added to the data source, as you've seen. You should rename these fields and groups with meaningful names. If you delete a control, the field is not deleted - you can drag the field back onto the form or right click it and select a control type to bind an existing field to a different control.
As long as your form is not in production, you can delete and move fields without too many repercussions. However, after you start using your form, if you delete a field or bind a control to a different field, you'll lose data.