I'm also in the process of building my first rack - and I can say that I've made a number of the same choices that you have (Disting, Clouds, Tangle Quartet).
From my travels on the various forums, I've learned to ask "What sort of music do you want to make" as a way to qualify any recommendations. Another question is "how many modules can your bus boards support". For example, I had a max of 17 modules that draw current on mine 
The things that jump out at me are:
There are smaller envelope generators around that you could look at, such as Pip Slope, which would free up some space. You are getting a really good envelope generator with Maths - it's possible this module isn't really necessary, but you have it hear for a reason, so maybe it is.
Clouds could be considered to have an echo function ( see http://mutable-instruments.net/modules/clouds/manual ); that said, the Synthrotek Echo is terrific. There's been some cool work combining it with a Ginko Grains oscillator you might want to look for. It's a neat pairing. My Clouds is on pre-order right now, if you want one, act soon. They sell out quickly.
I can't help but think that Braids and Warps is a little overkill at this point. I got advice to include the Intellijel Dixie II as a compact, characterful VCO/LFO. That said I've got my eye on both of them.
One area where everyone designing their first racks runs into trouble (and I"m no different) is leaving out utility modules, like Mannequin's Cold Mac or WMD/SSF Tool Box. I went with Cold Mac, but I'm also looking at Tool Box for my second set of modules.
You'll get a lot of feedback but at the end of the day this instrument is about what you want to do, so take everything with a grain of salt. If a module doesn't work out, the advice I've gotten is to put it down for a while then come back to it, as sometimes these technologies reveal themselves over time.
