I'd say 2x146GB/raid1 for esxi is true overkill. First, you loose one half of disk capacity just because of raid1. Moreover, for esxi you need just a few GB. I'd say raid1 with two small CF-cards is just enough, but it is up to you...
Concerning raid5: very simple formula says:
available_disk_capacity = (number_of_disks_in_raid5 - 1)*size_of_the_smallest_disk
So in your case from 6x300GB/raid5 you would get ~1.5TB useful capacity (not including what you loose because of formating and partitioning, etc).