I've yet to find a scenario where the Booster Cell should be set to intake, so definitely go with exhaust on it like you said
As for the Borg, it will both improve thermals for an open-air GPU as well as for the AIO (since no side is obstructed by your table).
As for the case fans:
- Setting them to exhaust will help the GPU, but leave your motherboard without active airflow over the RAM and VRMs
- Setting them to intake will help the GPU, but your motherboard will have active airflow
= unless GPU is heavily prioritized is suggest setting one fan to intake (the one right below/above the motherboard) and the other one to exhaust (the one below/above the PSU)
Hope that helps