You can move this topic to a more appropriate forum. See
https://www.eevblog.com/forum/blog/what_s-this-move-topic-icon-all-about/So you've got various pumps, valves and other loads that need to be controlled in sequence, presumably with some sensors, manual controls etc. that trigger various actions.
There are various ways of tackling this, depending on your expertise familiarity with industrial control systems and embedded systems.
The low hanging fruit, and probably the cheapest in terms of performance and satisfaction divided by time and cost, is to get an off the shelf pool control system and install it, keeping as many of your existing loads as possible, but replacing any that cause compatibility issues that cant be solved with a simple solid state relay.
Then there are various options based on wiring together off the shelf parts, mostly intended for industrial control applications. Take a hint from the Europeans here and get modules that fit a DIN rail mounting system and put a DIN rail in your enclosure, as then (most of) the various modules you need can just 'click' into place,then wire point point. You can get DIN rail mount relays, SSRs, circuit breakers and GFCIs, and even small power supplies. You'll also need something to be the 'brains' of the system. The easiest option here would be a small industrial PLC, but other options would be something Arduinoish, either with a PLC shield or with built in PLC style protected inputs and outputs, or a fully custom logic board of your own design. The major advantage of this sort of modular approach is that mains and high current low voltage circuits only go through off-the-shelf modules with safety approvals, and all wiring can be done in compliance with your local electrical code.
Then there's the fully custom approach of designing a replacement board to retrofit your old controller with, or possibly to standalone in a new enclosure, duplicating and possibly extending the old controller's functionality. However the old controller probably failed for a reason, and if it was corrosion related, its highly probable its due to moisture ingress and the old enclosure is compromised beyond economic repair.
In all cases you are going to have to maintain a non-condensing humidity level inside the new controller's enclosure. As its totally impractical to hermetically seal an enclosure of significant volume that is exposed to a wide temperature range, you will need some sort of pressure equalisation vent system that either does not permit moisture ingress (e.g vented to an internal bladder, + a desiccant cartridge in the main enclosure volume), or has provision to monitor the internal conditions and heat the enclosure as required to keep its interior above the dew point.