Hi! :)
So nice that you have documented your cactus journey...and sorry for the loss of 2 in the beginning..
I have some old photos of my babies....posted them somewhere I guess :) it was back in 2006 before the era of smart phones so I only had digital camera :)

Your buddy started to fatten up :) congrats!
Yes it is a good idea to try some part of it... just to make the stronger bond with the plant :)
You always leave the bottom part with the roots of course and top part can become a new cactus too as you did! :) For example you can split the difference in growth...in parts too :)

The sprouting is because it was trying to make roots, because leaning and because of stress (changing environment) etc...

I feel honored to connect with a brother sacred cacti enthusiast! ;)