In regard to the Gain, it only affects the "trem" signal. Very useful as trem tends to result in a perceived volume drop.
As to the boards, I do all the circuit and PCB design myself. I really enjoy the board design part - like putting a puzzle together. Also, lining up the components appeals to my OCD!
I then send it off to a prototyping service and they send me back 3 boards in a couple of weeks.
By physical separation, if you look closely there are actually 2 separate PCBs. One for the microchip digital circuit and one for the analog audio circuit. In that way it prevents LFO ticking to be heard in the sound. It's usually prevented with smart component placement. 2 PCBs are definitely an overkill but I did it like that so both the Pitch and Trem pedals I built use the same microchip PCB. Quite proud of that design choice!
Will try record a decent demo - sounds like any trem though