Making high frequency ram work seems easier on the R7 1700x and 1800x. I've heard a few reviewers saying they had problem with the 1700 in that scenario. So if you go for banana frequency ram, and other cooler than the spire from the 1700, I'd go for the 1700x with a bit of overclock.
For the storage, I would go for the 850evo over the MX 300 as according to Anandtech, it's much better SSD, But then, depends at what price gap they are you buy them. That is if you don't yolo NVME. Then the samsung 960 pro is a solid choice I guess.
Any X370 board will support an overclocked R7, so it's more a question of what you want on your mobo rather than what is the best, but if you have too much money and no braintime avaible, the asus crosshair VI hero has good reviews
The G.Skill flareX is ryzen optimized whatever that means. So if you want 3200Mhz ram, go for that, for less problems. I heard it will run with XMP profil out of the box no problem, unlike the ripjaws. 32GB max tho. DDR5 will proly be evented before you need more than that.