Regarding your first questions I would suggest you to review this KB article:
There is no problem to register a different path for your themes. In our documentation:
we have given a sample with:
App_Data and App_Theme are NET application folders and this is the reason why we recommended placing the theme inside these folders.
You could find useful information regarding these folders in the URL below:
However, this path might be different. Please note that once you have register a theme using the path above and you decide to move the theme, you need to go to App_Data -> Sitefinity -> Configurations, open AppearanceConfig.config file and change the path of the theme. (The other option that you have is to change it from the backend of Sitefinity Administration -> Settings -> Advanced -> Appearance -> Frontend themes).
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