Help an OW Beginner!

Greetings, This is my first post and I'm preparing for my first race so forgive me if I'm asking common questions that are already answered elsewhere in this forum: i missed them. To organize this thread I'm going to give a little history about my swim background, tell you where I'm at now, my goals, and then finish with a list of questions. Thank you in advance to anyone who takes the time to answer any question. History: I grew up swimming a lot as a child. Partly on various swim teams, and partly in open water (lakes and oceans). I'm very comfortable in the water. I stoppped swimming around 10 and didn't pick it up again until I was 16. I swam competitively my last to years of HS and was good considering my experience (probably due impart to the fact that I'm 6'5"), specializing in sprints--mostly butterfly and freestyle. Now: For the past few years I've swam OW with a friend 2 or 3 days a week for the duration of the summer. These swims have been pretty relaxed and span distances of a half mile +/- 0.25 miles. We usually take a rest around the middle of the swim, 30 secs-5 minutes depending on daily BS levels. I live across the street from both the beach and a 25m (maybe yards actually) pool but I don't use the pool since the ocean is free and more enjoyable. The Goal: I quit smoking cigarettes 2 weeks ago and I need a reason to stay quit. I found it: a 5k OW swim on Sept 29 (about 18 weeks). They are also offering 1k and 2.5k events.This week I started my serious training. 3 swim days alternated with 3 cross training days, followed by 1 day off. Swim training consists of 2 OW distance days and 1 speed day in the pool. Crosstrain day will be Run/Core days (I'm at about 2 miles now barefoot beach running and have body weight resistance exercises for core training after the run. These exercises were taken from a strength training for swimming speed book I found at a book store. I have extensive time to train. Questions: 1. Is my goal of a 5k race achievable in 18 weeks? This is a jump from .5 miles to 3 miles. Or should I aim for the 2.5k? 2. Can anyone recommend some good OW books to get me focusing better on technique, diet, training plans? 3. Suggestions for tweaking my current training plan? Or completely changing it? Honestly, I'd rather avoid the pool entirely. 4. I haven't measured my stroke rate yet, but I'm sure it's pretty low compared to OW swimmers. Should I focus on shortening my long smooth pool stroke? 5. Any tips from the veterans out there? 6. Should I join the local masters swim club. Note: I hate pool swimming but could probably use some stroke tweaking.