If I understand correctly, you want a macro userform as follows
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[[Load Schema...]]
[[Select Source sheet]]
[[New Mapping]] [[Choose Mapping...]]
[[Create XML]]
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Load an xml schema, select a "source" worksheet, and then to map the source worksheet columns or rows into the schema fields, finally producing an xml.
I propose that the "map" is done with an excel worksheet. So you press: [[Create mapping template]] (or [[Load mapping]] if one already exists, You then can edit it. Only if all necessary fields have been filled, the [[Create XML]] will be enabled.
The xml is then constructed according to the mapping and the schema, by direct code. (Not XSL)
It will take me 6 work days. I do not work on Fridays and Saturdays.
On day 1 you receive a working demonstration of the interface and a simple schema.
If you wish to follow my progress and issues, I can share a project management on Trello.
Since you did not specify what "other addons" you want, I can reply for those on a separate bid.
I'm Israeli and work during our day hours. You can google for Jerusalem Time world clock and see what time it is here. (GMT +2)