Does this mean one should only look for CPUs that support DDR4?
https://www.digitaltrends.com/computing/ddr4-ram-specs-release-date-future-computer-memory/
Who is using DDR4? Most of what I see for cheap is DDR2. Seems that must be why it is cheap.
Well, yes. Unless you have to upgrade your toaster, DDR2 has very little use. It's slow, and has inadequate capacity. Not to mention that to use DDR2, you'd need equally ancient CPU and MoBo.
Anyhow, DDR4 is good and all currently, but unless you're in a rush, DDR5 is coming out in late 2019 or 2020.
PCIe ver 5.0 has similar timetable.
So I'm pushing off my rig upgrade till 2020 or so, going for the latest and greatest with a big splurge.
As for storage, I generally have HDD for storing videos / smaller games / large quantities of stuff.
SSD with some 500Mbps read/write for larger games (games with install size at least twice the size of my ram) that have well designed asset loading systems.
And for large games which have suboptimal asset loading, the fastest storage I can get my hands on.