There will be some kits soonish for multiple units, but generally you can't put 5kW of heat in an arrangement like this [easily]. Coolant temps would be too high by the 5th unit, and the head pressure required to go through 5 sets of waterblocks would require pumps in series which is never a great idea. Remember the tube cross section is pretty low, so the minor losses become significant if you try and increase flow rate significantly - which is what you need to cool 5 units on one loop.

For now, the shipping on the second individual kit for now is only about $15, so you get the entire kit delivered for about $65.