This is one of those questions that you may get different opinions on. IMHO i would go for 10x system volume. So in your case it would be 3,100 gph. That could be 1 pump or 2 at about 1500 gph . You also have to take into consideration headloss due to verticle height , elbows , unions pipe length etc....
Some folks will tell you 3 to 5 times system volume. I like to oversized pumps a bit and the you can adjust them or tune them with a ball valve on the return line to tank.
This also all depends on how much your drains can handle. The larger the pipes the more flow you can go. [emoji4]
Another consideration is the type of piping. Pvc... flexible hose etc...
Hope this was helpful [emoji4]