i would want more than 2 nano pumps, even for a FOWLR
. the more flow you have (within reason) the healthier your tank will be. you don't want any uneaten fish food and poop to settle on the bottom or in the rock work before the filtration has a chance to remove it.
if you can manage that, you'll have a much easier time at the hobby.
i had a 40 breeder mixed coral tank that i had 4 x 650 gph
pumps in and thought i could use more. a pair of 500+ gph
pumps wouldn't kill you IMO
. they will blow the new sand around for a while, but that will eventually stop. or you could run one until you decide on corals.