Irrigation system for a large (still) empty plot

Regarding the overlap. Yes, the sprinkler must reach the next sprinkler. So with a throwing range of 10 meters, you have a sprinkler every 10 meters and not every 20 meters. With three units in a row as you described. This is the worst mistake in terms of coverage and homogeneous precipitation. Therefore, it must be strictly observed. At the sprinkler itself and at the end of the throwing range, the precipitation is the lowest.

It makes no (much) sense to go bigger than your pump connection. Only the pipe losses are lower. 1" is DN32 with about 25-26 mm inner diameter. DN25 is 3/4 inch.

There are huge differences in pumps. The Tipp are cheaper and have proven themselves in a few installations known to me. We use Wilo. When I think of well pumps, Grundfos is not the first name that comes to mind. But they have a name you pay for. Just start looking to see if you can find a pump that has more volume at the head and fits in the hole.

When using DN32 and the pipe lengths, I would plan the zones with a max of 2.3 m3/h. Proper pump and valves also assumed in 1".

The 450x is great. I installed it last year at my mother's. In your garden, it almost reaches the theoretical maximum area performance.

You can only measure discharge by filling a container. So let the pump run into a defined vessel and time it. Whether it is also the continuous performance will only show when the pump runs longer...

Control can be done via KNX. Note that you still need an additional transformer for the valves. But it is by far not as practical and easy as with a modern irrigation controller. Also not really cheaper. The only advantage of control via KNX is that you can activate several zones simultaneously. But that won't work for you because you can be happy to supply a small zone.... I thought about it for a long time with us and ultimately decided for KNX. But we can also run 2-3 zones simultaneously (pump at required head 30 m3/h).