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I ended up with 27 receptacles on 4 different 15A circuits. Each circuit has a GFI on the lead plug. Like others, it is mapped out so that loss of any single circuit only takes down a portion of the circulation system. I would suggest running every circuit to every wall, so that you always have a choice of which circuit you want to plug into.

Lights dictated more than 1 circuit, just on their own.

Do you have plans for a controller? I ask because controllers typically have powerbars associated with them. That powerbar goes into one receptacle, on one circuit and the controlled devices are plugged into it. As a result, you use only 1 of your many, many plugs and have a 7 or more things plugged into that powerbar. I have a LOT of unused plugs as a result of that.

Something I did right was to position the plugs high on the walls, where they are easy to access and they are away from potential splashing and dripping.

Finally, my mixing pump is an example of something that gets manually turned on/off frequently. For this, I exchanged a standard plug for a switched plug. That way, the pump stays plugged in all the time and I just turn it on/off like a lightswitch.