Setting up irrigation and we have 9 zones. In some areas multiple pipes go along the same trench for quite some distance. Later on I may 'T' off one of the pipes and I'm wondering best to label the pipes so I know which is which (especially if I don't know where I'll tee from yet.
Been there ,done that, not well. I recommend an "as built" drawing, accompanied by many photos of the open trenches , easy with todays phones. Be sure to include something in the photo to orient the picture, like the edge of a driveway. I put concrete donut protectors around most heads , partly to help find them . It is surprising how many sprinkler components are difficult to find after 5 -10 years. A poor choice I made was using 1/2 and 3/4 pipe , reducing size along a branch. So now repairs/changes require an inventory of both size fittings; 1/2 is good enough.Along the line you are thinking; at some point when I needed an elbow, I would put in a T with a plug, and for a T , I would use a cross with a plug for possible future use. I added ground level silcocks so soaker hoses or conventional sprinklers could be used. One thing I added later was drain valves at the low point of each branch ( ideally). A sprinkler system is a journey , not a destination. Also get several spare sprinklers if you want to keep the system uniform; the manufacturers regularly change designs. After a few years you will not be able to get matching parts. I use regular pipe, not the flimsy stuff they sell for sprinklers. If you have a second lower cost water meter for your sprinkler, consider putting some secondary lines in the trenches for hosebibbs out in the yard . Something to consider , with the outer blades removed from a rototiller , it will dig about a one foot wide trench several inches deep a good start for the pipe trenches.