If you are using fluorescent lights, you are probably doing the owner a disservice. I would design the lighting using LED lighting, which will give better control over the light distribution and may allow you to increase the spacing and eliminate some lights while still meeting your target illuminance.
If the ductwork is blocking the light from your ceiling mounted luminaires, that wall will look dark no matter how close you put the lights to the ducts. High angle light distribution to make the tops of a wall lit makes the space feel brighter and larger. It may be acceptable to have that wall dark, but the only way to get light on the wall (especially high on the wall) would be to mount some lights under the duct or on the wall to light that area.
The battery packs and exit signs should be on the same circuit as the general lighting, but connected ahead of any local switching. If you are using the circuit breaker as the switch, that approach would not work. Every time you turned off the breaker, the batteries would discharge.
Depending on the size of the space, I would recommend using LED lights with an inverter for the emergency egress lighting. I would use a UL 924 listed relay like a Wattstopper ELCU-200 or something equivalent from a different manufacturer to have the lights from the inverter follow the same switching as the normal power room lights.