Wow your space looks great! I can say having the big sink and sprayer next to the pots is one of my favorite parts of my system. You going with a single pot with a bag or basket?
I'm sure I could do 20g it just wouldn't be full volume. I would just add some extra water after the mash to bring me to my boil volume. But if I was planing to brew 20g batches I'd just get a bigger pot. Blichmann make larger heating coils for their bigger pots.
