@Ron_Wisp Installs like this are very complicated to asses with limited info from the deployment. So many factors come into play based on noise floor, channel availability, radio platform and even CPE types. From the looks of what you supplied you may even have towers in close proximity to others so this becomes a more in-depth design requiring a call as you already know.
To answer your specific question on the number of Horns facing in the same direction, that also depends on factors I outlined above and also depends on how much vertical mounting space you have on the tower. With our new Asymmetrical Horns having more narrow elevation cuts and absolutely zero side-lobes you are able to stack them vertically using down-tilt to project your coverage in front of another Horn in the same azimuth. For example you can use one Asymmetrical Horn with lots of down tilt to cover really close to the tower (0-1mile) and then another with less down tilt to cover further out (1-3miles) so those beams don't overlap but cover the same azimuth. The numbers I used for distance is to just explain the concept and are not exact. Basically you are able to build density now vertically as people have done for years with our Symmetrical horns horizontally due to our very precise antenna beam patterns. Make sense?
To answer your second question, again that depends on many things. The amount of guard band needed between channels varies based on the radio platform and its filtering capabilities. Some are better than others, but either way our Horns help no matter what radio you choose compared to old sectors with tons of side lobes. The other things is I would not depend on 4096QAM to help with speed on existing installs as the RX levels required to achieve that modulation rate will be huge and might require a new redesign as many of your fringe customers will not be able to achieve that rate if you are currently using 256QAM. If you are using something like LTU and running at 1024QAM, you can expect your distance to be possibly cut in half...
In the end, our Horns will allow you to achieve much more density that you have ever been able to do with sectors. If you keep your distances short and AP density high you will get better results, and like any antenna type, the more space you can put between them on the tower the better your performance will be.