yo
@leomarinho
For the first question, stack size is the biggest factor. Once you're down around 10-15 BB, you should start looking for good shove spots because you don't have much room to maneuver post-flop. That doesn't mean it's always shove-or-fold at 15 BB, but fold
equity becomes really important.
As for being the chip leader on the button, that's definitely a spot where you can open up your range and pressure the medium stacks. Any pair, most aces, most kings, and a lot of suited
hands can become profitable opens. Just pay attention to who's behind you—other big stacks can fight back, while medium stacks are often trying to survive.