If you are trying to do "tricks" on your bike, you should probably listen to the advice in those YouTube videos, but you should also be asking these questions in the Fixed Gear Freestyle forum.

But if you're riding your bike on the street, in more or less straight lines and with both wheels on the ground most of the time, the advice from others in this thread is correct: your frame should fit the same as any road bike frame (and there are LOTS of websites, YT vids, etc. on bike fitting).