DIY HDD Case

[SuperAn]

Hi,
I would like to make an external hdd case/ enclousure for two 3,5" WD Blue 3tb drives. 
I have space in my tower, however this is a noise reduction attempt. I want to be able to turn off the harddrives when I'm not using them. 
One hdd is used for my steam libary and the other for my media collection. 

Practical information, my mobo has an usb 3.1 gen 2 concetor, i can easely and cheaply buy an esata pci-add via aliexpress

Does anyone know wich interface has the least impact on speed for steam/gaming-use ? 
I thought the main advantage of estata was the full duplex capability, i don't know if gen 2 usb 3.1 supports this. 

Which kind of connector/interface should i use ? + details so i can order them online. 

thanks in advance.

SuperAn