the avalanche is coming! yeah I have a few more things that are coming in too. I posted my intended layout on my ebuild (for the lights and switches). It is almost like you don't know where to start. I am really glad I didn't tackle this project before I built the smaller control panel (I needed to learn some electric basics before taking on the big panel).
Those smaller heat sinks you have will need a fan from my experience (YMMV) - or do you mean two other sinks than the ones that commonly come with the SSRs? The sink itself was quite hot (some where in my thread I noted the temp) and I set up a fan to blow across them on my last control panel SSR life will be shortened. The one I bought this time shouldn't need a fan and the place I got it from on ebay is going to anodize it for me for $7!! All told 10x6x2 black anodized sink for $45.
What are you using the 1'' orings for? The lights/switches?
I should have enough DIN rail, but if you are planing to trow it out then let me know

You never know what idea might come up!