Bathroom Layout - Code Questions
Just in case anyone stumbles on this post, I got a few answers from my local building department. Since my local building department uses unmodified versions of the 2015 international codes (Building, Plumbing, Residential, etc.), their guidance should be applicable to many other municipalities. 

In short, the design I submitted was not approved. As the code clearly states, lavatories (i.e. the sink) must have a minimum clearance of 15" on either side, no exceptions. So, while there are many 24" and smaller vanities out there, if you put them in a corner, they will not be up to the 2015 International Residential Code or the 2015 International Plumbing Code. 

Finally, as it relates to my questions on the shower curb infringing on the minimum clearances for the toilet and the shower, my municipality was not concerned with this, they said they would measure the clearances from the glass shower wall. Other municipalities may differ, so always check with your local inspector.

Here's a plan of the design that I eventually got approved by the city.