I am considering following the IANTD training up to Trimix diver. From what I understand at the moment I would need to do Advanced EANx, Technical Diver, and then Trimix. My question is about regulators. If you move to twins with two first stages, how many second regs do you normally put on each first? Do you still need the redundancy of a secondary (octopus) on each primary? The same question applies to stage bottles - would these normally be configured with a first stage and one second stage reg?