I realize this after your 2 day window, but wanted to give some feedback about the event. I’ve swum the past two years (2015, 2016) and am registered for this year as well. It is a great event! Super cool to get to swim across the bay and under/between the bridges. It is well organized. I would recommend it to all triathletes from this area to do at least once.
Also, to soften the $300 registration fee – I believe the entire fee is tax deductible as a donation to the March of Dimes organization.
As far as training goes, my longest workouts were in the 6000-6500m range and I did some 1-hr straight swims to help prepare.
Let me know if there are any other questions I can (attempt to) answer for you.
Hope to see you on the beach.