Hi @Dominik. Welcome!
If SavaPage Server Requirements are met, it is feasible to install SavaPage on a Raspberry Pi. Please reply to this post to ask questions and share your findings.
SavaPage has a RESTful API. Feedback based on real world use is greatly appreciated. So your question is right on target.
To get a feel you can use the POST /documents/print API from your web application. This uploads a Standard File Type document to SavaPage, after which it can be previewed in the User Web App. At this point you can manually select a proxy printer to print the captured document.
A RESTful API to upload a Standard File Type document for proxy printing is not present yet, but could be implemented if needed. In that case the proxy printer ID and printing options like number of copies, single/double sided, color/grayscale, should be passed. Please reply to this post to discuss your requirements.