Welcome to the forum.
I can't help too much but can give you a link that I have had in my files from years ago pertaining to someone who was renovating an older Georgie Boy Pursuit. I don't believe it's the same year or floor plan as yours but generally of the same vintage. He has a series of videos showing what he did so it may or may not help you with what you're facing.
I'm not sure if this person taking you through this renovation is a member of this forum or not. And I'm also not sure if his youtube feed is still active or if you can contact him through youtube at this time but you might be able to explore that too. If you can get in communication with him some how, you may be able to get a lot of your questions answered ...assuming nobody else on the forum who owns a Georgie Boy of that era doesn't chime in to help you out.
Here are the series of videos from "rvliving7" that I'll link below ...again, these were from over a decade ago:
Great Motorhome Remodel video 1
Motorhome remodel 13 the finished project 99..5%
ah, I found the link to his intro page so I didn't have to link each video as you could have followed it from his youtube stream that he gives in the article below:
Motorhome Renovation of a Georgie Boy Pursuit Class A -- 4 July 2013 ...DoitYourselfRV
The "battery disconnect" switch is most likely what is referred to the "salesman switch" and that cuts the 12v power to the inside of the coach. It gets its nickname from when a sales person is showing the coach to a prospective buyer, as it's the switch they use to cut the 12 volt from inside the coach as they do not want the coach batteries to go completely dead if they forgot to turn something off when showing the features of the coach and it sits on the lot for an extended period of time until the next showing.
However, I've seen them typically located near the door because of that reason so I'm not sure if that is exactly what it is or not but somebody with a Georgie Boy can let you know for sure.
Oh, and if you haven't yet found the water heater, access to it is through the compartment immediately behind the right --passenger side-- rear wheel well (shown in image attached). There should be a small ring-like spring loaded cam lock latch that you pull on and twist to release the door ...see this VIDEO