420' Well 75 gpm Want to run through 1" pex, and other questions

First time user long time reader. switching to pex from copper, pvc, and fitted pipe.

Here is the truth I need to use my water, or I lose my water rights so I am setting this property up for my retiremnts day 15 to 20 years away. Going to put in fruit trees on a drip irrigation and a future house I will build myself.

I am having a well redone it had been abandon we just did a test pump and we were able to get over 100 gpm so that is good so here are my questions?

1. do I have to worry about the casing it was put in in 1950 and it is steal do I need to worry that it will cave in?

2. is there a problem with running pex from the well pressure related. Will it handle 100 gpm, I am using 1" pex, after about 500' I was going to decrease to 1/2 inch. Except for line that is going to go to my future house 3000' to 4000' away that will stay 1". Going to run 5 lines in different directions.

thanks

Jackson

Pex is not approved for burial. The lengths you speak of will require a larger diameter pipe. 1-1/4" is commonly used on a well only 30 feet from the house. Your idea of pipe size will not provide an adequate amount of water given the distances you state.

I strongly suggest PE (polyethylene) pipe instead of PEX, PEX is a bad choice because the ID is smaller than the same size of PE.