Thanks for the thoughts - it was recommended to keep the LR catalogue on a separate drive, however I am on the fence tbh - I don't want to have too many drives, config will likely be 1 or 2 M.2s with the 2TB SSD I already have, and an external back up drive.Looks like a good build to me! What was the idea behind the 500GB SSD and the 250GB SSD when you already have a 2TB SSD and a 2TB HDD? Personally I'd just go for a 500GB Gen 4 M.2 (either the Seagate Firecuda 520 or the Samsung 980 Pro) then just use the drives you already own or the rest. The CPU Cooler, is perfectly fine for the CPU, if you wanted to it could be upgraded. The PSU could be seen as a little overkill but it's worth investing in the PSU now as it'll last longer and cover you for upgrades down the road- the RMx 850W is a great choice and it's not something I'd change.
And as Martin said, they'll put them in the welcome box but you could always request the ones you need be connected for easy installation.
I don't want to end up throttling the M.2s either if they get full (Having that problem with a smaller SSD in my current build). I assume that would still be an issue with the Gen 4 ones, even though they are screaming fast?