how many pumps would i need?

[batang_mcdo]

up for this thread.
tank and sump is finally up and running, currently using only 1 pump, but planning to add another one

Will the water flo win this picture be good?

currently my 1 powerhead the return pipe has an elbow

but i noticed that the dirt doesn't get pushed.
will removing the elbow and also the sketch in my previous picture be better?
also would it be ok to have a 2 feet pipe going horizontally first before going into the tank? or will there be a big loss in pressure>?

 

[batang_mcdo]

up up Will a flowrate of 840 GPH be enough for my sump?
I would like to use the sump more for biological filtration. for the dirt, i'll just syphon them . currently still using 2 pumps which have a combined flowrate of 1300 GPH, but trying to save on electricity, will 840GPH be enough? i also have airstones in my main tank and a wavemaker . btw whats the effect of flowrate for biological filtration?