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My honest take from having purchased a pre-built a few years ago, and having built way over the top earlier this year...
Regal's build is almost the perfect build https://www.lfgss.com/comments/17213659/
I'm not actually sure that can be bettered in terms of cost / value trade-off, capabilities... the "go small, but make everything good" produces a hell of a good outcome... and that machine will likely sweep the floor with pre-builts at a similar price point.
CPU is always the worst upgrade... because it opens the door to a new motherboard, and at this point you're unlikely to bring many old components over, it's a path to just buying a new computer for sure.