I don't see anything in either code that prohibits it. P2705.1 of the IECC Residential code (2015) doesn't appear to mention it at all, and the UPC 412 (from 2018 at least) is about Urinals (whether or not a shower constitutes a urinal if you pee in the shower is out of scope of the UPC). :) UPC 408.9 mentions it this way: "Control valves and shower heads should be mounted on the sidewall of shower compartments or otherwise arranged so that the water does not discharge at the entrance of the compartment so that so that the bather can adjust the valves before stepping into the shower spray" So nothing to do specifically with the thing pointed at the door, moreso can you turn on the water without being sprayed by it, which is a good idea anyway since that first blast is likely to be quite cold.

You have a workable situation very similar to one we encountered a couple of years ago when we had a frameless shower door installed in a renovated bathroom. I would HIGHLY recommend that you have a professional do the installation from the measurement, ordering, and final installation. Due to circumstances I won't go into, an installer who did not make the initial measurements tried to do the installation for our project. He was unable to make the shower door work. To make a long story short, it took several months to get it right. The good news was that we had worked with a reputable kitchen-bath showroom who stood behind their product so we didn't suffer any loss other than the inconvenience of the delay. Had we been the ones who had done the measurements, I'm afraid we would have had to absorb the financial loss of a quite expensive shower door.

When I had the shower door guy out to measure, he made a point of checking how high the shower head was. Ours is on a sliding bar, so it can go up pretty high. We have a 6" curb and a 6' shower wall/door height, and it is fine with our standard 8' ceiling. Our "gap" is 18". Remember also that this "gap" benefits the air circulation in your shower to help dry it out so that you don't get moldy grout. Unless you have a very high shower head (very tall shower user) you should be fine.

Towel bar attached through glass = 1/2 inch. Be very diligent about proper structural framing on the walls on which the hinges attach, people tend to use any "bar / handle" (even on glass doors) as a grab bar.