The you very much for showing that the T318 is a viable heatsink for AM4 depending on the board. I have gotten it to mount on my ASUS B450-I Gaming using the following (ignore the M4 hardware and fan):
Four M3x20 machine screws
Eight M3 nuts
Dozens of washers
The backplate from a Noctua...
Hope to see how you progressed with the project. I am hoping to see this case and more coming out to fill out the niche of SFF that Phanteks and Corsair occupy.
The Seagate Expansion Portable drives are just Samsung M9t's with a SATA to USB 3.0 adapter plugged in. They are an excellent place to start and yes, I am speaking from experience.
For gaming, you won't need an i7. That is only if you need the extra threads (and heat) for content creation or virtual machines. An i5 will be just fine.
The G-Atlantic GA620 and GA630 may be similar to what you're looking to achieve. You can get it without an ODD cage and with a PCIe x16 riser and a dual slot and dual PCI slot cutouts. Information on the case is here: http://www.g-alantic.com.tw/1088/ga630/
It would take some modification to...