Product Showcase

 
The upper graphics card can be up to 369mm in length. Motherboards wise you can install quite a bit, as long as the form factor is ATX, Micro-ATX or mini-ITX. CPU cooler wise it can be a cooler with a height of up to 190mm, please do keep a note of that. You secure the graphics cards or other cards with a thumbscrew. At the front and rear side we can see one 120mm Pure Wing fan, it is included and installed for you already. In the topside upper mesh you'll notice mounting holes for other fans and radiator and/or fan solutions at 240mm max.

 
To the left you can see that you'll get 7 PCI slots to play around with so in theory you can house up-to two graphics cards in here, we'd recommend not more than two due to the compact chassis design though. 

Also, your maximum motherboard size is ATX, typically these allow for 2-way SLI/CFX maximum anyway. Albeit multi-GPU is not a thing anymore these days.

Mounting an HDD is simple, you mount the HDD in one of the two supplied trays, slide them in at the backside and secure these with the included (small) screws. The cage can be removed. 
 

Spread out over the backside you could mount up-to 5 SSDs btw. Not bad at all.