Grim is right you want to make sure not to bust off any roots, you can totally use 50lpm from the start BUT you HAVE to diffuse the air correctly so as not to cause too much agitation in the water. What I mean is if you have 50 lpm but you have that split between 3 lines and 3 flat disc diffusers in 1 site then the bubbles are way smaller and won't blow your roots off. You will not regret getting the big pump
@scubascrog also just add it to the air you already have going to your sites.