all plumbing/electrical/venting was done by me, in all the rooms at both houses....
hot/cold supply with main shut offs for the whole room and valves for each machine.....2 inch drain pipes or laundry tubs...quad outlets for each circuit breaker....
venting is usually 4 inch PVC pipe for each dryer......
all are natural gas, allows for more hookups versus 220 lines....more efficient as well....a straight horizontal pipe with "T"s for valves of each machine.......
as for HE machines, I can run them all at the same time....for a Neptune or Calypso, a few gallons is a quick fill....
..for standard TLers, water pressure can limit to two filling at a time.....especially time fill machines....
mostly never a problem for draining, just watch for them all draining at the same time, it may be a bit much......but usually I only have two TL going at the same time...
depending on your setup or collection, and your personal use, a second water heater may be needed/wanted ..... this has only been an issue during a wash-in, where the heater can't keep up....
each setup is gonna be a little different, just keep the basic guidelines, mainly diameter of supply lines as well as drains.....and don't overload an outlet/circuit