Hey neighbor, just a few thoughts after a few years of dealing with a few irrigation systems.

Until I get back to the office I don't remmeber all the formulas for pipe sizing so here goes until I can double check.

What else is tied into the system, How big is the preassure tank?

Use the 1" pipe to the poly pipe. Depending on what else is on the well you might consider 1.25" for the first 300'.

Asterperious