I would build it at first with 2 HLG-320's just for the case you really need up to 700w. If you can get away with only one driver and half as much light, perfect. In this case you already have another driver for a 2nd tower.
Usually we calculate 30-35w/sft to get 800-900μMol/s/m² at 12-16" distance. With 6-8" distance you'll see for sure +1000μMol/s/m² which is enough to add CO² to make better use of the light. With no CO² I would stay with 800-900μMol/s/m² to not stress them plants too much.
I would also LST them to at least 4 or more equal branches cause with single cola plants you don't get a closed canopy covering all the available space. The gaps between the tops would get wider and wider the higher the plants grow. Maybe its best to FIM them as soon as they have etabilished to create lots of twigs. But you would need at least a week or so to veg them a bit before you push the bloom switch.
The more I think about these towers the more I like the idea. I like the saying, "there is always enough space also in the smallest hut" and with this setup one can use the available space to the highest degree.
I've also though about a vertical system as the F-series strips came up(2017) but to mimic a HPS-system with center cooltube.
I thought about covering all 4 sides of a 4ft, 6x 6" alu tube with lots of double row F-strips. The inside of the alu tube gets additional U-channels glued on over the whole length to create lots of 1" high fins inside the tube to allow better heat convection. 6" fans on each side in push/pull configuration to blow air thru the tube. 3 DR F-strips on each side of the tube, 12 strips total, driven by 2 HLG-600H-48B to make it dimmable down to off.
Would be a fecken bright 4ft "360° bulb" with ~1300w LED which could replace 2 vertical 1000w bulbs easily. Easier to hang up and rotate it and you add a trellis in a certain distance to the tube(20" to all sides maybe). One could arrange the plants around the trellis and let the twigs grow thru it. So exactly the opposite of what you plan to realize..
One could also create smaller tubes with less strips. Cooling works pretty good this way cause you need only ~20cm² per LED watt with active cooling and without lens covers half of the heat will be dissipated on the outside anyway so 10cm²/w on the inside is already enough to keep the tube well below ~50-60°C. And cause the plants are arraged around the tube you can easily LST them without doing any changes with the setup. Access from all sides every time but the plants needs to grow big with such a system to create a closed canopy around the bulb before you push the bloom switch.
So its more a setup for growers having only a licence for a limited number of plants.