Hello Specki
since I built the street myself with 3 men within a week (costs about 10,000 euros, man-hours, materials and machines) I went all out. 90cm excavated, reinforced L-beams on the right, thick foundation on the left, filled with RCL, gravel on top and "Knochensteine". For you, excavating 20cm and filling with suitable material would certainly be sufficient. You could support the development with appropriate channels. After all, you want to build.
Steven