Definitely want access to the panel (guessing s building code issue as well)... keep in mind that you'll probably have some maintenance to the system over time.
When we first moved here the piping was in place and I didn't have any options to move things. Replacing the thermopile on the previous heater (needed about once a yr) was a contortionists nightmare. Accessing the filter drain or a nearby spigot was a one-legged procedure... so when I went to rearrange my set-up; I laid things out where I wanted them for access foremost & then set about determining the best piping route (limiting elbows, where to place valves, unions, etc). Don't forget to keep in mind things like flow rate for heaters, chlorinators.
Best of luck as you plan for the upgrade.
Respectfully,
