Those DIN rails are the ones I used in my build and are a little flimsy but do the job considering they're not readily accessible.
CB's, RCD's or RCBO's are a cheap safeguard for both circuit and operator and don't add much to the overall cost of your build. Sure, you could rely on your meterbox but a lot of old places still don't have RCD's in place. They're not really a viable alternative to a switch though considering their location inside the enclosure.
Like Mofox I used mechanical relays to supply active to my SSR's. I wanted to be able turn the elements on and off easily and didn't want too much current running through the switch contacts.
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Edit: better add some pics.

h34r: