1. Yes, Threadripper 1900x is pretty much useless as it is still an 8 core CPU like a Ryzen 7 1700(x) or 2700(x), the only advantage is more PCIe Lanes and quad channel memory.
And also Threadripper would make for a better video because you could show how to insert the CPU into the socket. Yes, that is special. And you need a screwdriver for the installation (According to AMD, comes with CPU).
But you had to get at least the 12 Core (1920) - wich wouldn't be much more expensive but give you 4 Cores or 8 Threads more than you have right now. The 1950x is at around 763€ and has 16 Cores, the 12 Core 1920x is at around 526€
The i7-7820k is at around 450€ so around double the Price of an older Ryzen 7 1700. The 2700 (NEEDs 400 Series AMD Board or a BIOS Update for wich you need an older CPU) is at around 275€ right now...
2. Best Bang for Buck would have been a Ryzen 7 2700 or 2700x - with a decent board that one would be around 200-300€ cheaper than what you got.
The i7-7820k is just eating electricity and runs hot as hell while only being an 8 core/16 Thread CPU - the same as a Ryzen 7 wich would cost almost half of that.
3. I think storage could be important and a higher end Board could make sense - because of the m.2 Slots it comes with.
What I'd do for a high end Video Editing thingy would be two 512GiB NVMe SSDs, maybe 1TB _AND_ an additional S-ATA one. With the latter only looking for good price/size ratio. A 128GiB is totally OK for it. It only needs to boot Windows. Working you should on the NVMe Drives. And use one as the Source and one as the Target. Like in the good old days with the 3 HDDs: One for Windows, one Source, one Target.
4. THe Power Supply doesn't look too good either. I think its an old, group regulated thingy.
For a System like that you should looked at 80plus Gold or better Platinum units with DC-DC (well, almost all do that) with an LLC-Resonant mode converter. The nominal efficiency of a somewhat decent PSU these days is 90% and voltage regulation is in the 1% area, 2% is considered not that great. And Ripple we are talking about something like 20mV or less on all rails with really good PSU...