I happen to be working on a similar budget.

Intel is DOA for the next couple of years, so it is AMD all the way.........

Case -Rosewill Challenger (ATX case - any will do, a case is a box to hold your parts.) Got mine on sale for $60.

PSU: Rosewill Hive 750 watts - I'd recommend any 750 watt PSU that is rated 80 Bronze. Got mine for $40.

Motherboard: ASUS Pro WS X570 Ace - Best Ryzen Motherboard available - accepts ECC memory - added bonus - No RGB.

CPU: Ryzen 2700 - 8 core/12 thread which will hold you over until you (or anyone else) can actually buy a Ryzen 9 3950X.

Memory: Crucial 32 GB DDR 4 3200 ECC Ram sticks (Start with 2 - the 2700 can only accept 64Gb max, then get 2 more when you get your 3950X.)

Video: AMD RX 5500 - Will drive a 4K panel, same performance as an RX 580, but only draws 110 watts, and will be 2/3d's the cost.

SSD: Sabrent Rocket 1Tb - PCIe 4.0 Write speeds of 4,000Mb/s read speeds of 5,000Mb/s OS/Apps

HHD: 4Tb HGST (for data) - cheap, very, very reliable. - I am currently using 4 2Tb versions in a raid 5

Motherboard thoughts: The Asus MB is the best MB available for Ryzen 9. It is specifically designed for workstation solutions (and a number of boutique PC vendors are using it). It supports ECC memory, which I consider to be mandatory if you actually value your work.

Ram thoughts: The correct answer to the question "How much Ram do I need?" is As much as the board/CPU can address.

SSD/HD drive thoughts: NVMe PCIe 4.0 is the way to go - every second counts.

Video card thoughts: Nvidia's cards do not age very well - each generation tends to lose driver optimizations as Nvidia releases new generations of cards. AMD on the other hand, will continue to provide driver optimizations to a wider generation of cards.

As an example, the latest Adrenaline drivers still support RX470 (My boxen will have an RX 480 - picked up an 8Gb version for $75), so even 4 year old cards are getting support. That can not be said of the Nvidia 9 series.