Hi Russell-
There are a lot of variables to consider, for sure. One thing that jumped out to me is that you do not need as much PSI as you are figuring. My irrigation runs on about 16-17 PSI, and functions perfectly. The sprinklers that I use are these 'mini-wobblers'. I run 6 per 100' 1/2 inch line. I can run three lines at a time no problem. Here is a link-
http://www.dripworks.com/product/Q_MW
Water filtration will be a major consideration from your irrigation ditch. To minimize pressure drop and frequency of cleaning, I would recommend as coarse of a mesh filter as you can use (lower 'mesh' number is better). I would use a 2" fliter to minimize pressure drop. Here is what I use, and like-
http://www.dripworks.com/product/Q_FAMCP
Dripworks is an excellent company. I would definitely consult with their experts on your system. Setting up a commercial account with them costs nothing and gets you wholesale prices (30-40% discount). I have worked with them for years with nothing be positive experiences. They know their stuff.
If you have more specific questions I would be glad to try and help, but really, I would go straight to the pros and get some good background ideas.
good luck!