Case is subjective, but put good quality with good airflow on offer..(you can add rgb fans if you want to brighten it up if so desired)
Used a X570 tomahawk mobo as can then have 2 gen4 nvme's if so desired
Got 3 below just so you can see price differences in price etc(can have 2 on board). Reason I put the Firecuda ones in there..5 yrs warranty(others have that), 3 yrs data recovery(others don't). Also main reason is the endurance of the drives. The 520 2TB comes with a 2800 TBW, the 2tb 510 just below at 2600 TBW...the 520 1tb has a 1800TBW and 510 1tb has a 1300TBW if you want to go cheaper at £139...so endurance on these drives are really good. Not sure how much data will be moved around, but if he's using it for work and is a games designer etc, guessing will be a fair chunk of data flows...if not, then can downgrade the nvme's(As a comparison the SN850 1tb has a 600TBW endurance, the 2TB version 1200 TBW, SN750 1tb and 2tb 600 and 1200TBW also and SN550 1tb and 2tb are both 600 and 900TBW
32 gb 2x16 Ram is sammy b die so best you can get for 3600C16..was £179 and they keep alternating betw 199 and 179..I'd ring and see if they can drop it again
5900x for 12 cores(can be had cheaper)
decent psu with 10 yrs warranty, more than enough and s/b efficient at the lower loads..The new RM850X(new 2021 version) is better but £129, but has greater indurance in fan. Psu is more than you need, just allows a future upgrade in a few years etc
I just stuck a 6600Xt which will be great or 1080P gaming, or try and nab a 3060tiFE(download telegram on phone, sub to 'FE PartAlert' etc)
Forgot to add a cooler for CPU..Brocken 3 above more than adequate imo
So money can be knocked off, esp. on the nvme part(take off 520 tb and you're already below the £2k threshold), but just put the drives with greatest endurance for large amounts of data flows( and put gen4 for speed also). Don't know how much storage your brother needs also, as you could go for different board that takes more nvme's if you wanted more of that kind of storage, or add some sata SSD.
My basket at Overclockers UK: