6 gallons is correct... an easy way to calculate is 1 gallon per 3 lbs of grain.
Mash and lauter is easy when you get the hang of it.
Mash as above, drain and measure.
Sparge with whatever makeup water is needed for the pre-boil volume.
Keg #1: Brown Bomber Bourbon/Oak Vanilla Porter
Keg #2: The Bollocks ESB
Keg #3 Lawnmower APA
Bottled: Mjolnir Mead, Lazy Daze Hefe.