First of all, 76 is very warm. In fact, if it rises to 78, you will not even be allowed to use a wetsuit. If I was in a wetsuit in 76 degree water, I would probably overheat. It will only be cold to you for the first 50 or so yards.
What are you asking for?. A 300 yard swim is not that bad either, unless you don't know how to swim, in which case, i reccommend going to a pool.

Bike-Don't worry about it, it's your first tri. but if you keep going, the most important thing you will need is gears. worry about that before aero position. (and it's a SS right, not a fixed gear, because you will not want to do it on a fixed, but it is possible.)

You might want new shoes and don't skimp on them.

Have fun, you will be able to make it fine, don't worry about how fast for your first tri, just try to get through it.