[bernstem]

Throw distance can be reduced on most heads. On rotors (e.g. Hunter PGP, Rainbird 5000), reducing throw too much can negatively affect uniformity of irrigation. On rotators (e.g. Hunter MP rotator, Rainbird R-Van), reducing throw has minimal effect on uniformity.

 

[bernstem]

The pipe slanting up doesn't matter. Second floor plumbing supply lines run straight up in most cases without issues other than some minor pressure loss.

Not having a backflow is very bad if you are using the same water supply for irrigation as for your drinking water. Almost every municipality requires a backflow preventer to protect the city water supply. If you are rural and on a well it may not be a county requirement, but you risk contaminating your drinking water without one unless the drinking water and irrigation water supplies are completely separate.

 

[bernstem]

That seems a bit of a weird layout to me. I would worry the corners without heads wouldn't get enough water. I would do an irrigation audit to see how even the irrigation is.

https://content.ces.ncsu.edu/landscape-irrigation-auditing-made-simple

45 feet is a long throw for most home rotor heads. They tend to max out at 35 feet which is why he probably staggered the 45 foot sides like that. With limitations on the throw distance, that might have been better with 9 heads in a grid (maybe with rotator heads which have 20-30 foot throw depending on model), but cost would have been more.