8700k is a really REALLY good chip, it loves to be pushed hard so definitely get an AIO loop or do your own watercooling setup.

If your Mboard has 4 DIMM slots just get 16gb RAM and upgrade later if needed. If it only has 2 DIMM slots i'd do what WBOX40 suggested and get 32gb.
5 accounts really doesn't need much RAM. I'd also stick to a regular high capacity SSD as an NVME ssd offers no gaming benefits at all.

btw I think the MX330-G case is nice. Everything that has been suggested will fit inside it supports ATX full sized motherboards so go nuts!