I've been wanting to do a tiny-PC build for a long time. At just 3.7-liters, this is about the smallest tiny-PC you can build yourself (I don't count retail tiny-PC's like the Intel NUC or the Zotac ZBox). Having a M.2 NVMe O/S drive is an amazing boost even over my last SATA SSD (a Crucial M4). Using an OEM Samsung MLC-type M.2 NVMe PCIe-3.0x4 drive saved me about $30 over buying a retail equivalent like the Samsung 970 EVO Plus (which uses slower TLC NAND coupled to a faster and hotter I/O controller to provide similar speeds).
Some people get weird about the difficulty in finding firmware updates for Samsung OEM drives but Lenovo regularly comes out with a SSD firmware update utility which recognizes the Samsung OEM drives I've used (SM961 and PM981; SM-series is MLC and PM-series is TLC) and it's a free download that works on any system. Samsung's Magician SSD utility doesn't work on OEM drives but Magician doesn't do anything impressive or really useful anyway and retail laptops have gone without it for years now.
Microsoft has monetized so many features in Windows 10 that they practically give it away (easy enough to turn off all the spyware features during installation). Microsoft's Media Creation Tool made it a snap to create a bootable USB flash drive and activation only required my previous Windows 7 license key (a free upgrade then).
The 8th-gen i3 is now a quad-core part and the entry-level i3-8100 is faster and cheaper than a 7th-gen i5-7400. It even out-performs 6th-gen i7 models on some benchmarks and so, for the price, is an easy choice. If you MUST have 6-cores, then the i5-8400 is half again as much at $195 (vs $115).
The MSI B360I board costs less than the Asus B360-I and there are reasons why. The equivalent Asus board has a nicer BIOS, a 5V addressable RGB header (instead of 12V non-addressable), HDMI 1.4 (instead of DVI-D), a USB 3.0 Type-C port, a SPDIF Optical Digital Audio port, and Intel I219V LAN (vs Realtek RTL8111H-C). MSI Mystic lighting with red LED's is not nearly as nice as Asus AURA with that board's addressable RGB LED's.
The MSI B360I is fine if you want to save a little money and don't need the extra features of the comparable Asus B360-I board which is better (and more expensive). Just make sure you can live with the compromises brought on by saving a little money. I'm happy with the money I saved but you should know what you're giving up by paying $40 less.
Absolutely flipping brilliant! It's cheaper and faster than a Samsung EVO 970 Plus.
Obviously, get the "u3" variant with USB 3.0 ports. I think this is a great case overall but I wish the PSU was more like 110W even though I've never had any problems with just 90W. The built-in USB 3.0 header has thick, stiff, and overly long cables which eats up more room than it should (tuck it behind the mobo where there is extra room).