I'll just randomly add some thoughts to some of the questions comments above. im about 65+hrs in if the timestamp on the saves are correct. I am also playing on normal if that matters too.
For Zones, I tend to clear as much as possible too, although there is a small issue with that in that you tend to almost out level some of the later zones.
For equipment, generally the way I do it, is for my inq, I usually use crafted, and mix of drops and crafted for my other party members, and because I tend to want to clear our a zone, I can craft items for my other party members
For Dragons, if you are on level you should be find with on level gear, if you are under level, then you may need crafted gear as it will tend to have more stats than the drops.
That being said, I have killed 5 dragons so far, two of them I soloed with Blackwall once you get the patterns down, use guard.
Skyhold upgrades, yes they are vastly underwhelming, sure it opens up a room in a tower for templar or mages. I would have through you would see some visual differences. Even doing the keep customization in the Undercroft does not make much impact other than maybe the throne.
Performance for me has been fine, I have had a few pauses but that is generally in skyhold exiting from solas' room to the outside
Companion story for Sera without spoiling the details too much, I pretty much had her at the point of leaving/telling her to go and then all of the sudden, we are pretty much buddy buddy to the point that her character select card has changed.
I read that they do, but did not notice it much with other. had not paid enough attention to those. I think Dorian's is changed too, have to look at an old save