my 550 has a 1mx2ftx2ft sump and works well BUT I only have 1x drain line and 1 return line 5000LPH, I would aim for a 5x2x2 sump and a 16500 LPH laguna pump for that tank. you may want a wave maker in there just for added flow.
How you do the drains etc is all up to you, you could use 1 hole for a return line and the other 2 holes for drain lines.
Id just run one pump, if you set it up correctly it shouldnt matter if the pump breaks the sump should hold all the excessive water, only advantage in running 2-3 pumps is if you need set flows in certain devices for example you run a UV that requires a flow of 2500-3000 LPH getting that flow by Ting the return pump off with a valve wont be easy.
there are many more negatives then that one pro which is not really a big pro for freshwater also.
How you do the drains etc is all up to you, you could use 1 hole for a return line and the other 2 holes for drain lines.
Id just run one pump, if you set it up correctly it shouldnt matter if the pump breaks the sump should hold all the excessive water, only advantage in running 2-3 pumps is if you need set flows in certain devices for example you run a UV that requires a flow of 2500-3000 LPH getting that flow by Ting the return pump off with a valve wont be easy.
there are many more negatives then that one pro which is not really a big pro for freshwater also.