[Van down by the river]

My experience was with a full temperate system with a temp of 50-55C
and we have more humid weather here. The range would be less drastic for you. I don't think you will have a problem.

If you want to be sure, call a local company that provides live seafood tanks. If you can't find one. I suggest you take a thermometer and a tape measure to a local seafood restaurant, check room temp,tank temp, and glass/acrylic thickness. This should give you a better idea.

As to the critters, I would believe that there are comparable species filling the same ecological niche as their tropical cousins. You seem the type to do your homework so I think you'll be able to uncover what you require.

I will not likely be going into the ocean in the near future. otherwise I'd offer. I was thinking of suitable tankmates:
Bay Pipefish Syngnathus griseolineatus
Gunnels Pholis sp.
Sculpins Cottidae sp. Always check the sizes, some get big!
Sailfin Sculpin Nautichthys oculofasciatus
Grunt Sculpin Rhamphocottus richardsoni
Snailfish Liparis sp.

I've found many small flounders (size of quarter) and shrimp(5-10mm) in sandbar tide pools that I couldn't identify ( I have to admit I didn't try hard). the shrimp could serve as a food source for larger seahorses.