Water extraction points / water pipes / irrigation in the garden - ideas

What do you mean by branching off after the box? The circles are always (behind the respective valve). You still need to plan the pipes for the drip irrigation.
Place the sprinkler at the terrace all the way in the corner.
Otherwise, it looks solid. It’s only final when the garden and irrigation are finished. They aren’t lasers after all. A few centimeters here or there don’t matter.
An automatic irrigation system is great. Once you have it, you definitely won’t want to do without it anymore.

What do you mean by branched off after the box? The circles are always (behind the respective valve).

That the yellow pipe makes a T-branch in DN32 after the distribution box. Otherwise, there are T-pieces between the pipe and then it goes smaller to the sprinklers.

You still have to plan the pipes for the drip irrigation.

The supply lines are in black. How the individual beds will be made is not yet finally decided. Therefore, it is important to me that the DN32 are planned and laid first. Unfortunately, many things are done step by step with us. Or rather, only when one step is finished is the next step looked at and planned on site. It also changes quite often.....

Place the sprinkler at the terrace all the way in the corner.

You mean at the top right at the terrace towards the garage? The lawn does not go right up to the garage wall there. Something else will go there. Or do you mean a different position?

Yes, I meant above at the terrace/garage. Use DN32 everywhere. Only the short section from the circuit line to the sprinkler is smaller. I would also change something about the routing. Not everything in a line but for example, at the blue circle at the height of the garage/terrace, branch off to the other side. You do need more end caps, but you have a more homogeneous pressure distribution.

I would also change something about the pipe routing. Not everything in a straight line but, for example, at the blue circle at the height of the garage/terrace, branch off to the other side. You do need more end caps, but you have a more homogeneous pressure distribution.

So you mean something like this?

Yes, something like that. You could also push it a bit to the right. It should only prevent the pressure at the last sprinkler from dropping below 2.8.

Should a PE-HD pipe actually lie in a sand bed? It will be better, but is it absolutely mandatory?