I have looked at paperless in the past and just asked why? I just spent a little time setting it up to see what it was about, then I spent hours configuring it and my email server creating paperless email addresses that other emails forward to! I cannot believe I have lived this long without it.
I posted my paperless backup strategy here: https://lemmy.world/post/46429607
As for retention time, in digital I don’t care. Storage is cheap enough for that amount of data.
Paper I tend to only keep very important documents, but haven’t done a full inventory scan yet.