I put my ATC rack along the back, starting at the back right.
For me, preserving the full 48" width was the most important factor in the placement. I often leave material overhanging off the front of the machine.
I opted for the side-entry tool forks as they allow for larger diameter, and longer cutters.
The holders are spaced as close as possible together to maximize tool density- but it comes at the cost of dust collection. While I have never tried it, I think if you needed dust collection to work, you could install a tool in every other fork, and it would leave enough clearance for the dust collector head and brush. Collectors that retract the dust hood, like Ugly Dog’s sidekick also accomplish this.
I noticed the pneumatic chuck on the spindle can be quite sensitive to the orientation of the tool holders to ensure a proper pickup. I made my rack adjustable so it’s possible to dial in the holders so they are parallel with the spindle.
I posted more in-depth information in this thread.
