good luck in your bread making adventures! it can be highly frustrating when it's not right but highly rewarding when it is. I believe you will get there!

the reason I said that I thought it was under proved is when you get large holes (marked with red circle) with a dense crumb (marked green) then that's a tell tale sign of being under proved. if the large holes have looked like they have collapsed it's over proved.

in terms of hydration, every different brand of flour will have a different protein content, depending on which breed of wheat, the farm it's from and how good the season was. it will dictate how much water to use. so I suggest you go with your instincts and have a play around.

after watching the vid, I think what could have happened to you is either your water was too cold, the yeast was old (so not as active), or both. so you could try using warmer water or getting new yeast.

from the picture it looks under proved and that would make it chewy. next time I suggest let it rise longer. also if you add more salt for flavour bare in mind it acts as a retarder, so you will need to prove for longer