what size of sump for a 75 gallon

[mossman604]

what size of sump for a 75 gallon, and do i need a protien skimmer, the 1 i bought has bio balls miracle mud green alge a heater and thats it, is this ok
it is huge like 4ft long, too big for me. id like to build a small 1 for under the tank in the cabinate area. any thoughts. im bringing the tank home within two weeks and want to be prepared. thanks