I’m no expert, but I learned a lot about spa jets and flow rates for my ongoing build as I’m incorporating different kinds of jets that require more flow (25gpm). It seems most spa jets need about 15gpm each so 90gpm total for 6 jets. For most pumps, 90gpm is doable and in line with the limits of a lot of the pool equipment. In my research most filters, heaters, SWCG have a max flow rate of 90-120gpm. You can check the flow diagrams/charts in the manual of your pump and it will provide the GPM based on pump speed (rpm) and the head loss (dependent on your equipment setup, elevation change, plumbing distance and angles, etc...)
8 jets on a single pump in line with all of your equipment would likely provide only about 10gpm per jet and not get much therapeutic pressure hence the comment above. A dedicated pump without all of the other obstacles would be able to deliver stronger flow. The issue is that you still need to be able to provide filtration, heat, and sanitation to the spa and don’t want another set of that equipment.
You can go with a dual pump configuration that uses shared equipment with a more complex plumbing and valve configuration at the equipment pad, or have 2 sets of returns for the spa. I opted for the later. I have a set of 6 returns tied into the standard pool/spa pump in line with all of the other equipment and a separate pump and suction for the JetArrays.
Regarding the spacing of the spa jets, I have the same OCD tendencies and it looks much worse in this stage with long pipes sticking out but you have to envision the finished product. With Gunite and the pipes cut back flush with the wall, the differences maybe less noticeable. Add in the water, plaster, coping overhang, waterline tile, etc... a 6” difference is going to be less obvious. For our spa, we have 2 jets close to each other with different bench depth, this is where my wife and I plan to sit next to each other and has the best view over the rest of the pool looking back at the house. The rest of the jets are spread out. I think having a mix might be good so people can choose jets close together for a couple or spread out for 2 bigger guys that want their own space.