[JoJo]

i'm a beginner myself so take my suggestions with a bag of salt. I would only go as big as a 1", i think if its any bigger it may have too much air & not enough pressure to feed the outlets(i would make the outlets 1/2).

I would put the union as close to the pump as possible & the valve directly behind it(opposite of the pump) because that less water that would drain out when you seperate the union.

i'm sure others will chime in, i hope, i dont want you to rely soley on my suggestion