if you redshirt a guy and his WE drops from 51 to 46 and he says in the email "I was a little upset...", can you leave that redshirt on and not expect much consequence? or should you activate him?

In my opinion, that WE drop is not too bad. I redshirted a guy who gave me the "Not Cool" email, he dropped 15 points in WE. He made about 20 points in overall improvement plus some IQ improvement in his redshirt season. He is playing in his second season and his WE has improved some, but haven't gotten it back to his original level. But overall I was happy with the outcome as he wasn't going to play much his Frosh season anyway.

That’s not a bad drop, he’ll make that back the following season w/ major minutes and/or a start.

I would not take the redshirt off, that is a pretty small drop.