Hey OP, I may run into you eventually, I'm currently doing the 3.40's in my challenge.
Your early game seems good from watching that video. I start to shift gears when it's down to 6-handed, and start with my stealing hands. If it's 25/50 and not 6 handed I will make a few steals maybe from late with good hands when no one has entered the pot.
Once you reach 50/100, if I'm below 1200 (8M, 12bbs) it's push/shove from there. If you're above that mark, then it's stealing hands when in position and no one has entered.
For example, your ATo hand at 15:10 I most likely would have stole with just because you're on the button, no one has entered, and it's 25/50 mark. But I don't think it's a complete leak for folding. I normally raise 4xBB at 25/50 and switch to 3xBB at the 50/100 level, but I've learned from 2p2 that on the button you can raise a bit less at the 25/50 (150 instead of 200) since they may not respect your hand as good anyway.
The biggest part is maintaining your chips for when it gets to push/fold mode, and remember the gap principle, AT, A9, can be great to shove with from late, but often I will fold AJ to an early raise unless you have reads on opponents.
I play 4 at once as well, and am constantly checking previous hands in the hand history to see how players play hands, and the types of hands they play. I color code people based on how they play, not their ROI.
Green = Loose/Dumb
Teal = Very Passive/Weak
Red = TAG
Light Blue = Calling Station
Orange = LAG
I'm interested in seeing how you play middle game steals and push/fold.
Good luck! I'm sure you can do it