Welcome to the forum boone, and thanks for the pics. Worth a 1000 words as they say.
It looks like you have a very good start. Sorry I don't have much knowledge about pump sizing but from what I have learned, with a 200' run to the house you may need to use 1 1/4" lines for your feed and return.
The idea of bolting on the back side is very interesting, maybe a bit more work and expense drilling all those holes and buying the hardware. But it might be useful for future repairs.
It seems that most of the builds, mine included have a much closer ratio in fire box size to water jacket. My water jacket is 47" and firebox is 36", as seen in my build thread. I am not saying which is better because I don't know. My guess is you will have longer burn cycles to get your water up to temp but maybe it will be more efficient over all. It will be interesting to find out.
It seems that I have more questions than answers. Like what and where did you get that 52" flanged pipe from. Also what is the small pipe or nozzle pointing up towards your flue pipe.
I'm also curious about your flue pipe being 3" off the bottom. I have mine about halfway down into my firebox but maybe lower is better. You can always cut some off if needed.
Are you going to have a fan forced draft and how and where do you plan to put that?
This site has a wealth of knowledge available so please keep us posted on your progress and go through old threads to learn as much as you can. I know I learned a lot here and many helpful members helped me with my build as it went along.
By the way what part of the country are you in?