On the fundamental side... where are the envelope generators? A couple of Tip Top Z4000 ADSRs would go nicely here. Each stage can be modulated and there are pots to control the level of the envelope as well as invert it.
In the 1U world. Why do you have the 1U reverb with a nice ErbeVerb in your rack? Ditch that little thing.
The line out 1U... get rid of it too. It's just not worth it. You have two line level ins and out assuming you're in an Intellijel case.
With the space saved on the Line Out and Reverb, put in another Quadratt. You'll thank me later.
That 16 space hole is perfect for an 8HP Ornaments & Crime and an 8HP Temps Utile. I love them because they are SO multifunctional and EASY to adjust. The menus are very simple to get through once you understand how to navigate.
Are you really in love with the Rain Maker? It's a lot of real estate and relatively expensive. Plus I believe they are backordered. 36 HP can be filled with a lot of love as far as effects. Unless the Rain Maker is integral, I would save it for a larger version of your build. Tough choice.