Just finished uploading some unsolicited evidence covering the time from our initial filing until the end of 2023. This was roughly 4 months of new evidence since we filed in September. Going forward, I think every 6 months could make sense, but I'm still on the fence about maybe just continuing with 4 months at a time.
The upload was split into separate files covering different types of evidence during the period. Each file had footers with the petitioner's (i.e. conditional PR's) name, period of evidence, type of evidence, and page numbers (1 of n, etc.). The 12mb limit per file is pretty reasonable, but I did spend some time fine tuning the Optimize a PDF settings in Acrobat to make sure the quality wasn't degraded.
My only piece of advice to those submitting multiple files would be to upload them one at a time. That way, you can make sure they appear on the list in the order you want. The most recently uploaded files appear at the top. I didn't heed my own advice and tried uploading 5 files at once; this made them appear on the list in the random order they finished uploading, which is slightly annoying after trying to be thoughtful about how to name/number everything.
After having gone through the experience of putting together the first batch of additional evidence, I think it will be smoother the next time around.