Relandscaping questions

The previous owner thought she was a landscape architech. Most of the fixed are pretty straightforward but some issues I want feedback on.

The sprinklers are currently in-ground hoses leading to the plastic heads on stakes. I want to replace them with PVC and connect it to the existing zone system. I also want to lay new sod so my thought was to rototill the whole yard, dig the trenches for the sprinklers and lay the sod on top. Am I looking at this too simply?

I have a DIY sprinkler system (local law requires irrigated front yard - yep - CA).
The flex hose (crap #1) is about 6" (crap #2) below grade.

Some of the heads are actually above grade - ans that is using the cheapest 2" head at HD.

I saw some pros digging a circuit - a bit more than knee-deep. They were working in midday sun at approx. 100 degrees F.
These are the workers the GOP wants to deport.

Get a trenching machine for the PVC - min 3/4", use 1/2" risers.

Rototill first, then trench. Figure out how to get the heads on and install sod.

My first thought is to wonder how deep the hoses are buried and whether tilling the whole lawn will reach the hoses and chop them up. But I suppose if you want to replace them all a little chopping up won’t matter.

most of the hoses are on the surface