I often send "thank you" emails to stations that give me QSO confirmations for hard to get states. Thus far no one I've exchanged emails with was offended or put off. In fact I've established some friendships that way. I would encourage it. But I only send a thank you email for states that have been really hard to get, which for me has been North and South Dakota and a few states in the North East. ;-)

On only one occasion was I involved in an email exchange setting up a FT8 sked and it was mutually beneficial for us both. I personally wouldn't be the least bit offended if someone requested an FT8 sked with me. I'd be happy to accommodate. I know others might disagree and that's cool. As long as one is not breaking any rules or inconveniencing someone else I wouldn't see the harm in it.

Gene
WB7RLX