Do I expand abbreviations at their first use per section or per paper?
This is an IEEE publication, but I haven't come across any specific instructions.
I would do it per paper, unless the paper is extremely long and some abbreviations are defined (and used) in the start, but not used again until 20 or 30 pages later.
It's okay to remind a reader what the abbreviations mean, but avoid annoying the reader by being overly and unnecessarily repetitive.
The standard is once per "document," whether that's a report, or a book, or a journal article. However, longer documents will typically come with lists of abbreviations and symbols; many journals also do this. Even then, it's still better to define it once in the text first:
standard widget units (SWUs)
before using it again later.