You are overthinking a lot of this:
Does he have a shield/how much flow does he have?
------Better question: Is his flow bar white? or grey?
Are there minions nearby?
------Simple answer, yes. Better question: Am I in the jungle? if no, there will be minions.
How many Q charges does he have?
Better Question: Is the graphic displaying his 3rd Q showing? Late game, just pretend it always is.
Does he have his Ultimate?
Simple answer is Yes, unless I actually just saw him use it this fight.
All these calculations aren't calculations. They are things you can easily notice. Yasuo is not hard to shut down, and when he is behind he is toast unless you stall the game and let him farm. If that happens, its lategame: its Yasuo's turf now.
Try to counter pick him: Olaf works great, so does Kayle. An AMAZING Yasuo can outplay you, but it is very difficult, especially if you are good with those champs.
Have your Jungler camp him/tilt him. I try to share this tip with junglers all the time as a top lane main. If we kill the enemy top laner, and we are still healthy, don't go far and kill him again as soon as he gets to lane, or even between his towers if able. Especially in lower elos, (like where I am at) this can make people rage quit or TILT super hard. It seems like a dirty trick, but if you are playing ranked, its all fair game.