I never really thought about maxing out the pot. The most grain I have used was 16.4 pounds, and that took around 7 gallons of mash water. It fit. Brewer's Friend seems to think I should have used closer to 5. I'm using 6-gallon Torpedos as fermenters.
As for sparging, I just squeeze the bag. I thought avoiding the sparge was part of the beauty of BIAB, so I chose not to do it. I've been back at this for two years. I moved to BIAB one year ago, and I haven't sparged since.
Until just now, I had no idea what "boil rate" was. I looked it up. I didn't know it mattered. No idea what mine is. I keep the kettle boiling, but just barely. I use Fermcap.
It wasn't until last month that I made any effort to figure out how to measure the volume of the wort. I use a tape measure. About 1.15" is a gallon. I used to hit my number and then pour whatever I had into the fermenter.
Usually, I end up with a wort that's a little heavy and not quite 5 gallons, so I dilute it with hot water until I get my number. I just figured that was the way. At least once, I've had a little wort to spare.
It usually seems to work, so I haven't been motivated to change anything. For that matter, I use my HBS's crush, I never ask how far apart the rollers are, and the gravity seems to come out right. I've seen people here talking about the importance of getting the crush just right. Maybe I'm really lucky. I did miss on the low side with a heavy ale last year. No idea why.