5k Swim training plan?

Don't over think it. Just increase in yardage and get ow experience. I started out training for a 5 miler as an experienced swimmer at 9-11 k yds a week. Bumped it to 2 x masters of 4k a week and a long swim of starting at 2 miles and adding .5 mile or so.every week. Or start at a mile and add from there. Really sort of depends where you are starting from and how long you have to get there

I can add I've completed 2 IM distance triathlons with 2.4 miles times around 1:05 to 1:10. I am comfortable in OW but won't have much opportunity to practice in OW as the race is in January in FL and I live in VA. I train in a 50m pool.

So training for the extra .7 miles should not be much of a stretch. You won't need to worry about nutrition.