Agree, don't add the ice bath unless you feel the bottom of the bowl while finishing your drizzle and it feels hot. As long as it is close to body temp you're ok. If it feels hot when you finished adding syrup than add the ice bath or retard in the freezer for 10 minutes like @foodpump suggested.
Sometimes the butter is too cold to add, so if your bowl is cold to the touch then go to the warming method. You should not be able to add your butter in cut chunks (not soft enough)
I did look at the youtube.
Although a very good video, I have 2 things to add.
1. I personally would suggest to divide your first granulated sugar. 300gm. for the syrup, and 100gm. for you egg whites.
For the egg whites, start to whip. When they start to become cloudy/opaque add the 100gm. granulated sugar. The addition of sugar to the egg whites will reduce you chances of deflation greatly.
Remember, this is just me. Some will disagree. But I have made this a couple of times.
2. I believe the youtube showed the use of a rubber spatula. I would recommend not to use anything rubber or plastic. It is porous and has a tendency to retain grease no matter how much you clean it. I would use a non porous spatula like silicone
Good luck and most of all, have fun.
It seems weird, but baking turns out better with a positive attitude.
When you mix or put something in the oven to bake, always think it's going to come out great. don't be cautious(keep watching, opening the door to check, etc.)
edit. the youtube showed taking the syrup off at 230F. this is ok especially if you have to set it down for a moment. the syrup will continue to cook after removed.