Your box is looking VERY tidy and I've been watching this part of your build with a keen eye for ideas since I'm +- at the same stage with mine. Well done!

Can't advise you on the suitability of the SSR but I also got a 25A one (not the same make/model as yours) and I was unaware that it would still pass current when off so I exchanged it as faulty only to find out the new one does exactly the same. On mine its enough to light a 220V pilot light dimly an if I recall correctly I measured it at around 12V or 14V when in off position. For what its worth the guy at the shop told me to put a BIG heat sink on it if I plan to run 25amps thru it.