Hi Steve,
The equipment you take along is entirely dependant on the environment and planned dive.
There is often a lot of "lively" discussion regarding pony bottles, "two of everything", etc. But one of the things that concerns me with this approach is that the redundancy gained by a pony bottle can create a false sense of security and could lead to doing dives that would otherwise cause the diver to stop and think. I'm not "anti-pony" or "anti-redundancy", just examine why you feel that you need the redundancy.
As far as training and certification for solo, I'll echo what Walter said, and go one further: I really do not think "solo" can be taught. I do not believe there are any unique skills, secret handshakes, or magical equipment configurations. You should already have mastered the skills needed to dive in your local environment before considering solo.
My opinion is that solo is really just an application of basic dive skills, minus a buddy at your side. You are now responsible for all the planning, situational awareness, navigation, the works. I don't think there is a magic number of dives or a certain certifcation level to acheive before you are ready to solo.
For my own solo diving: I use the exact equipment configuration that I use on buddy dives. I usually do not take a pony. If I am planning a dive that I feel that a pony would really be required then I'd rather have a buddy on that dive.
Again, your equipment choices will depend on your environment, and what works in Hawaii may not be appropriate in other places.
Best wishes.
