Tuck, V-ups, Russian Twists, Hollow Hold

I came across

 

www.gymnasticbodies.com/proper-way-v-ups/

 

and this video

 

www.youtube.com/watch?v=1RwgqYQpWp8

 

from 6:10 s (appx) onwards.

 

The article says to go slow and controlled, but in the video by Durante, he goes really fast. ( ). So what do I follow exactly? And what am I missing here?

 

Also,

 

www.gymnasticbodies.com/first-things-first-mastering-hollow-body-position/

 

How far should I lift my upper back with my lower back pressed in? I can press in my lower back with my upper back on the ground, so, should I be lifting it up till I feel only my lower back touching (or) till just my lower back and bones (I think scapula, not sure) on the back keep touching (or) else I don't know how to do it.

Master the movement slow first. Requires more control and stabiliazation so is more taxing on the motor system and more beneficial for learning. Speed up once you have the slow movement mastered (probably a few months).

Have to dash to work so can't answer all questions or view videos right now, will let others answer