1. you can't overdose stress coat or so we are told but I don't think fishes like swimming in pure stress coat add it when you change the water in the container
2. Dr Axelrod says for bacterial tail and fin rot, add acriflavine, wait 3 days, change the water for fresh water, wait one day, do 3 days of acriflavine again.
3. If you want - might as well when you do the water change. Probably soothes the sore bits on the fish, has a healing action and treats the water too.
4. As per 2, but if the water gets scummy or the fish seem (more)distressed you might have to change to fresh water sooner.
5. Keep it isolated until its better, and so you can treat it easier
+ Dr Axelrod says after treatment if the finrot is advancing you might have to snip off the rotting bits with a sterilised pair of scissors to avoid the infection spreading. hopefully won't come to that. He says if it is already super-severe amputate the rotting bits and then do the acriflavine treatment
Best of luck!
+ They're gonna need lots of air to cope with this, make sure you have an airstone in there although not so much air that they are getting buffeted around