Sara,
First of All:
Welcome to the board...
I'm new to spearguns myself and have found that there aren't a lot of people around here who want to talk about them. You can use the search function on the site to see some of the other threads on this topic that I've started (or tried to start) recently.
I started an Email conversation with Andre Biller and he invited me to call him to talk about guns. I did so and he was very informative and did not push a sale at all (he doesnt sell direct). I then found one of guns (48") on sale at an LDS, so I bougth it for $150.00. It was the .48" sepcial wooden with 2 bands and a 6mm shaft.
I have stirred up some good conversations with avid UW hunters who suggested the 48" range for beginning.
I have oof the reason made good sense to me, some of them sounded like Ol'timers rejecting new technology. Either way, I took the advice, at least for the time being.
I ordered a 115 centimeter gun by Sporasub from Diveinn. It listed on most sites for over $200 and they had it for about $75, so I jumped on it. It is a single band, and it is a B**** to load.
As for your questions about length, power and accuracy... I'll defer to someone iwth more experience.
Good Luck.