The idea is going for raid5 so that should be around 100TB of storage, minus the OS and apps, etcs. But easily 80TB+ net storage.
I use a 1tb ssd for the os/apps with my raid5 strictly for storage. Kinda nice if the os needs to be reinstalled or I want to migrate the raid cluster.
That’s also a good option but I wouldn’t with 6 drivers personally. I have a 12 bay array with two pools of 6 each running raidz2. I’ve run raid 5 for a long time but have had one drive fail many times and always have mini heart attacks while I wait for the new drive to come in and the rebuild process to happen.