Re: number of boxes
I am a hobbyist in the High Desert and I provide them double deeps year round. For me it's not about harvesting honey.
Regarding how much honey stores to leave is a regional thing specific to your immediate climate. Bees need the honey to eat throughout the cold, non-nectar season. If you do not leave enough stores, they will starve. I do not believe there are drawbacks to leaving too much.
Regarding the amount of room that you leave. You have to provide for the amount of bees you have going into winter, any empty space gives the bees more area to police and maintain. Leaving unguarded boxes could lead to winter damage from pests and such.
These are good questions and I am looking forward to seeing some of the replies you get.
“Everything will be all right in the end... if it's not all right then it's not yet the end”