Hi, I didn't have a lot of room either so know completely understand! I won this aquarium from Algae barn last year and it was for the Cade 900. I had to ask them to downgrade for me, but if they weren't able too - I would have made the 900 fit somewhere without being able to open doors .
Nothing on the right is needed/required. I ultimately bought the Apex for my system, so I am now only using these switches for a second heater and sump light. My apex energy bar is in a media cabinet next to tank and I found I like having the extra room to manage better (cords that come with pumps, heater, light, etc. are very long). I do use the board for my controllers, which I do like, but not a requirement. I have average size female hands and can reach back switches with door open about 4 inches, front can squeeze in about 2.
For plumbing... I'm not smart enough to know how it all works

, but this was one of my big concerns and reason I stopped hobby 20 years ago after my sump overflowed from power outage while at work. Currently, I turn off my entire tank to do water changes and my return pump daily to feed. It will siphon from the return a little bit (not the intake or weir) but does not overflow sump or come close to it.
I hope this helps, when I was looking for new tank (pre-contest), having more Cade 600 info. out there would of been incredibly helpful. The Cade support at Algae Barn is also the best, they were ultimately able to help me with anything I could not find online.
All and all, gorgeous solid tank!!