A few little things that I see (you may still be working on them, but stuff that looks a bit off to me at the moment)

Why do you need caustics? Nothing in there really would warrant them. No light is passing through an object, and casting onto another. Refraction, sure, but I don't think there would be any visible different with caustics on or off. Plus it will speed up your render.

The elbow shader looks way too shiny. The brass looks to me like a really polished bowling ball. You should also texture the spec map so it doesn't look like a perfect mirror. You should also take a look into gamma correcting your file textures. Since all renderers expect things to be in linear color space, and most images we see on our screens are in sRGB space, you need to convert them. You can do this through Maya's color space workflow. Look up "linear workflow with maya" for more.

The glow looks way too strong. Glow is usually added in post, and not in your 3d render, as it's faster to tweak. The quality is usually better as well.

It's looking nice otherwise, nice job.