Seriously, I know all about those fears! About the PoPs, there should be ones every couple of miles. They will also be available at the start of the race so, if you can, get there super early so you can go as often as you need to. Check the course map and drive the course beforehand. You may see some bathroom options that way as well. I just walked a half marathon last Sunday and our course had us going through two parks - both of which had real bathrooms, woo hoo!
One thing I've read about hydration is that it's most important to drink water the days leading up to a race. On race day, unless it's hot and/or humid, you can limit your water intake to a few sips beforehand [with your fuel] then drink along the course as needed. As always, practice your hydration on your long walks so you'll know what your body needs.
Also, about being a walker, again, I know all about these fears about being the only one. Yes, I do end up at the back of the pack...this time I finished fifth ..... from last.

But, if I keep a steady pace, I can pass others [runners, even!] who zip off ahead of me at the very beginning. And I will only improve.
One thing that also helped me was to look at last year's results for a race I've signed up for. That'll tell me how long it took for the slowest racers to finish. I'll also look for the number of participants in a current race. If there are several hundred or more, that's a good thing - it will mean a good range of abilities and paces. Just try to start at the very back so you'll be out of the way of the speedy ones.
As slow as I've finished, I have never encountered any volunteer or runner who has been anything less than wonderfully encouraging. They seem to be moreso with me because they know I've gone way out of my comfort zone. Now, if they'd save me a banana or two, I'd surely appreciate it!
I hope you have a wonderful time at your race. Jeff Galloway says that one of our goals for any race is to finish in a way that makes us want to do more races. And I hope this race will make you that much more excited for the PHM.

You are so smart to do this race now - your nerves will be much calmer for the Princess.
1. Yes, it does. If you use it as a real watch, it stays charged up for several weeks/months.
2. I don't know. Wanna go on a research trip to find out?
Yay - I really do like it and hope you do, too.
I have a friend who has organized a lot of conferences and uses the first come/first served principle with her registrations. When she compared runDisney's way of doing things to a conference registration, it made sense that the early birds did get the worms. It was enough to convince me, from here on out, to register on day one for any of their races.