The L4000 won't work AT ALL for 4 x GPUs, unless you use single-slot stuff like the AMD WX series or the Galax "Katana" models.

 It only has 7 "peripheral" slots, you need *2 each* for most current GPUs that are worth mining on.

 For more than 4, you're looking at either VERY high priced cases, or custom "mining specific" cases that still tend to be high priced.