Why did you choose galvanized pipe? Is the manifold to remain above ground?
were doing it all over again, I'd use Sch 40 PVC with Sch 80 fittings, and place the whole manifold in one or two valve boxes in gravel below grade. Save the galvanized for the above-ground stuff. At least if it leaks (it won't with PVC), you've got it draining into gravel.
Also, depending on what kind of sprayheads you're using, you might want to add a pressure reducer. Rotors for mid-size throws (+/- 35 ft radius) are made to operate at 50 psi, but smaller pop-ups run ideally at 30-35 psi.
Although, I assume that since you have a lake your yard is fairly large?
Your choice of sprayheads might
be limited by your flow rate, though. What is your GPM from the pump? I would guess it's adequate if you're getting 50 psi thru a 1-1/2" pipe.
BTW, Congratulations - no more walking around with hoses!