quickie open water prep

Next month I will be swimming Lake Tahoe with a relay. Expected conditions are 55 - 60 F and wind and chop, with no wetsuits allowed. Fortunately we will be swimming only 1/2 hour shifts separated by 2.5 hr (6 person relay.) Also, there will be a boat that I hope is big enough to see with by bad eyes and close enough to pull my frozen carcass out of the water. But I am very nervous. I am a pool swimmer who likes his water 79 +/- 2 degrees, and this will be my first serious open water experience (without fins, mask, and snorkle in the Carribean). Is there a chance of cardiac arrest if I don't prepare correctly? Will it help if I hop in the Pacific ocean a couple of times (the temperature is comparable right now, I think.)? Or will I only be making myself uncomfortable? Am I better off not knowing what I will get into? I know (in theory) about earplugs and cap, but what is the grease that I hear people talking about? What kind and where should it go? I don't have a lot of insulation. Will those big(ish) mask/goggles keep my face warmer? Is it better for the boat to hang on my breathing side, where I can see it, or well ahead of me where I can lift my head up to sight it (no drafting allowed, of course). I know I wander if there is no line under me while I swim. My brain tells me that an in-shape swimmer will not become (seriously) hypothermic after only 30 minutes, but I would like someone with experience tell me that, too.