Go 1" poly all around for laterals. Burial depth is kinda shallow for my liking. I did mine at 12"+.
Laterals are already buried. I'm not redoing the whole system. 3/4" is fine for 3-4 sprinkler heads. 5"-8" is all I could do with a shovel, and then add 550' of digging in total. A ditch-witch or pipe puller is/was too big to go through our yard to get to where we need it.