Of course you can stand up before the blind gets to you, just like in a live cash game. Just make sure to Unclick the auto post blind, and sit out when it asks you to post your blind.
No penalty if you’re quitting the game. If you need to come you have to post both blinds (just like live cash game), or you can wait till the blind gets to you again.

That’s always when you leave the table. Right before the blinds. No reason to leave right after the blinds, when you’ll have position.

Of course not. That’s exactly when you should leave. However, in order to join a game, you will be forced to pay the blinds, regardless of where the button is. This way, people can’t abuse the system and keep leaving right before the blinds.