I am actually a bit surprised that page-break-before: right is supported for some font sizes. The fact is, we are not really working with pages here, but reflowing data. How to determine when to hit a white page on the right side? Most of the readers do support 'page-break-before: always'.
Just a quick remark, try to refrain in defining sizes in pt. Main reason for that is that those cannot be changed by the readers. If you keep it in em or %, the users can use a larger font or smaller font if they desire.
Sigil is not a mix of ePUB2 and ePUB3. You misread the source. Sigil is an 100% ePUB2 editor. However, it will not automatically delete some ePUB3 elements like audio and video. That is a big difference.
Regarding printing, that is why I say that printing can be a challenge. The format is not intended to be printed.
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