Well you could mount the cards with risers in a large PC case in a creative way if it has to be stealthy. There are very wide mining motherboards with 8 PCI-E slots where you can directly mount 8 GPUs, but they are weird, kinda expensive (compared to old used hardware) and can be problematic in Windows.
As for risers, just make sure to not buy the ones powered with SATA as they are prone to fire and other fails. Molex-4-Pin should be fine if your PSU can handle the load, otherwise go for risers with a PCI-E power connector and power them with a server PSU + breakout board. Performance and stability should be fine if they are built correctly. Buy from reputable mining shops instead of eBayor Amazon if you are unsure, slightly more expensive but they won't sell you shit.