You're very young to be undertaking these changes!! Good on ya! Lol
I have a 79 Surfside
that I will be working on soon. I would like to move our fridge
down to where the heater is too, to create more counter space, however; my wife doesn't want to have to bend over to get things out of the fridge. Also, we've been camping in feb/apr in BC and the heater proved to be a valuable item that we will keep. If you do move the fridge down and remove the cabinet, you should create support for the roof to eliminate a sagging roof. Also, it appears you had a roof vent at one time in the middle of the trailer. You should consider re-installing another one that opens/closes. It's an important feature to reduce condensation/moisture within the trailer. There are good articles on this site to instruct how to create roof curbs for your roof vents and how to deal with potential water issues.
I'll be following your thread for ideas so take lots of pics of your work!! Good luck!