I'm less than 2 decades behind you, retired, and have a 1500g system with a 560g display tank. I don't want to say the bigger you go the easier they are. But the bigger the water volume the less worried you need to be about staying on top of things. I have lots of automation, I am a lazy reefer. 2 Years ago my Dad had a heart attack and I walked out the door for 10 weeks to take care of my Dad. Other than a heater failing, and a CO2 tank going empty the tank ran without issues for the 10 weeks. And when I got back home I jumped from a 20lb CO2 tank to a 50lb and solved one issue.
My Dad is healthy again, and today is his 80th birthday. He spends alot more time and physical energy maintaining his 2500g Koi pond than I do on a 1500g sps system.
I would say the only critical issue is the dimensions of the tank. Don't go too Tall, or too high on a stand, that you have to contort your body to get in and out of the tank for maintenance.
A year ago in an emergency we had to swap a 400g for a 560g tank. The new tank is 120x30x36. And that 36" height is killing me. The tank is beautiful, but I can't reach anything in the bottom 1/2 of the tank. Even with an assortment of tongs. Even mounting a clam on the sand bed is a 20 minute flury of foul language and yelling. We are trying to arrange to install a 120x60x30 tank and hopefully that will get rid of the hatred of heights I now have.
At some point health is going to come into play. So plan ahead for that with your automation. Can your tank run 2 weeks without any help from you? Look at that as your minimum mark. Build everything for 2 weeks. Also build everything for an idiot. Invest in a commercial label maker and start labeling everything.
Every pump has a label identifying it where it comes out of the water, and again where it gets plugged in. Every automated outlet has a number and a label identifying what gets plugged into it.
My system is in 4 locations and has 5 dedicated circuits. I have multiple GFI outlets in each location and each GFI is an audible GFI so it beeps when it is triggered.
You have to plan for an instant when you are away and you have to walk a dumb neighbor thru fixing something on your system. That's why you need to label everything.
Also make friends with 1 or 2 local maintenance people. It's worth wasting some money now to pay them to do something trivial on your tanks so they are familiar with them. And then when you are in a bind and away from home you have someone that has some idea as to what they are looking at.
Any of those lil things that you know how to fix - I jiggle this, I smack that, this outlet doesn't work - Get rid of all that crap - Any new equipment invest in better quality because it will pay off. I use Jebao prop pumps in my frag tank, but I also only expect them to last 9-12 months. I use Tunze in my display tank because they last as long as I keep my cars.
Dave B