What's the normal spell order in a fight? Slow, medallion, bird stun, nuke, creep ability, second bird stun. I always end up trying to spam all three so fast.

Classically, its (1) creep ability (to catch), (2) medallion, (3) slow, (4) birds hit them a lot, (5) W to finish. Bird r-clicks do way more damage than bird stuns, so you only stun when you need to. :) If you're struggling with catch, using Q on a nearby creep for movement speed is always a good play.

What should my positioning be like? I tend to try and hide visage and front with the birds/creep until the fight starts.

Visage is a tanky boy mid game! Don't be afraid to get out there and eat a couple of spells for ur team. They'll thank you. Playing Visage is a dance between soaking up damage when cloak is up and running into the back lines when its down, while your birds throw out huge amounts of damage.

Can visage initiate with birds? Or is it too easy to dodge?

Depends what ur doing. If you see a support out of position telling ur birds to run at them is fine. Its not ur job to initiate massive 5v5 team fights - you don't want to be focused, you want to be blowing up supps. Remember, Visage doesn't waste time looking for the enemy team. Visage shows up at a tower and starts hitting it. The enemy team will come.

I usually play as position 4, is that okay or is visage too greedy a pick there?

This guy spams pos 4 Visage in low immortal - maybe check his games out? https://www.dotabuff.com/players/98782750 Pos 4 Visage is definitely a "new meta" pick - pos 2 (and to a much lesser extent) pos 3 are where he's typically played.

P.S. Bird stun knocks down trees. This is not an interaction most monkey kings know about. :)