My reasoning is as follows: The first NVMe is the OS one, I dont want to touch that for many years, so I dont want to get a small drive. For the second one, this is the one that will be swapped whenever I want to upgrade in the future. So getting 1 TB now is fine as, by the time I filled both NVMes, I would have enough to just remove the second one, replace it with a larger capacity high speed one, and then maybe just sell it to get some value.When it comes to RAM, if you're needing a significant amount, one option is to buy the PC with the cheapest RAM you can (1x4GB @ 2400mhz) then purchase your own RAM to put in. I don't believe PCS sells 64GB as there was stability issues with 3600mhz when Ryzen 5000 first came out and they just haven't added it back.
For game storage, there isn't really a recommended speed. All I say is just make sure it's on SSD, the time differences for loading aren't huge between SATA and NVME, but with Direct Storage coming soon that could change.
DDR4 build looks good I'd still personally go with my storage setup though
Also, do you know where I can request PCS to bring back the 3600MHz 64GB for the alder lake builds?