I'm very happy it helped, in that case.
If this is a gift to your nephew then I'm going to highlight a couple of things. Firstly, you can definitely add in more storage later. What I listed out is a light professional set up (imo). But you don't necessarily need redundant drives for mirroring. You do if you're a professional with a deadline and losing money by the hour due to a drive failure. If not, then you can just order a replacement when (and probably
if) you ever need one. Plus as I said, you can always add more drives later so you might want to keep my advice about the NVMe drive for the main OS drive, but pare down the other drive suggestions to just putting a 2TB traditional drive in there. Or a 1TB SSD. Both would be fine for someone who is a student learning this stuff for example. So if that's the case, you can save a few hundred right there. Just make sure when you're calculating the size of PSU that you need, you account for what you might add later.
My advice about a good monitor for professional work stands,
but monitors really do have a variety of competing needs and you wont be able to just spend more and more until you get a monitor that is good enough for everything; anymore than you could spend a lot of money to get a vehicle that was both a good van and a good commuter. The technology doesn't exist to make a monitor that is an excellent photo editor and an excellent gaming rig at the same time. So make sure your nephew's expectations are what you think they are. Gaming monitors don't need excellent colour reproduction but it does need a high refresh rate. Gaming monitors don't need 4K resolution (though gamers say they do.

) but something for video editing in this day and age pretty much does. (Because you're expected to produce 4K content, these days). What I'm worried about is, because I don't know your nephew's age and goals, they might want to be messing around with Doom or something and you give them a monitor designed for photo colour balancing. There are compromise monitors. I don't want to have advised you to splurge on something that would actually be disappointing to them. If they intend to use this for gaming, I'll give some more balanced advice. Ultrawides are good for video editing, btw, because you can get more of the video timeline horizontally across the screen in your editor (bottom half of the screen image below):
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Based on my impression that your nephew is getting this to learn on rather than immediately begin earning money, I'm leaning towards a suggestion of getting a previous generation Threadripper build. It should be plenty fast enough for serious work, it will mean you don't have to skimp on RAM or storage and will leave you a bit more money. It does mean they'll be on the wrong side of the PCI-E version chasm which limits upgrade path a little. But in all honesty, there's always
some component you're buying at the wrong time with computers. And the thing is, they depreciate fast. With computers you have to shake the mindset you have with other big purchases like a house, a fridge, etc. Buy a high end fridge and seven years later, you've made your money back twice over compared to buying and replacing a cheap fridge twice in the same time period. Buy a high end computer today, and seven
months later, there's something better available. My upgrade cycle, if you're interested, is every five years with occasional interim purchases as useful in that time, and I work professionally in computers. So don't go all out with this if his goal is to learn rather than meet deadlines.
Also, he will probably want Windows. RRP is a bit expensive but there are grey market sources where you can buy a licence which they've managed to sell lower through some bulk interntional deal or other. Works fine and not illegal, just not how MS want you to buy them.
UCD Keys
You'd better also check he doesn't just want a Mac. But you get a lot less bang for your buck usually with those and there's a growing number of creatives moving away from that (though the M1 is bringing some back).