Now first off as far as the OWS:

Just keep getting in with your wetsuit on. Skip the bay, get in the lake. It took me 2-3 times to get comfy in my wetsuit when I got it last spring. Just push through it. If you can do that distance in the pool, you will be ok in the open water. Swim parallel to the shore so that you can stand up if you need to.

Secondly about the knee. Have you tried icing? I have had tweaks over the past 8 onths of training. Ice has been a huge help. try starting back with a walk run schedule. Are your shoes worn out?

Thirdly, if you have to walk during the 5k, so what? Is your goal to finish the race, or to try and place ? Lots of people have to walk some portion of the run.

Lastly, have fun and enjoy the day.....