AMD will release new CPUs soon and while I think Ryzen 3000 will hold up in the future, either Ryzen 3000 prices will drop or Ryzen 4000 will offer you even more performance for a similar abmount of money. So please keep that in mind before buying right now.
I think you are in CPU, main board and GPU upgrade territory, but $1.8k would allow you to buy a new, high-end PC. If you so wish.
One without many compromises imo:
8c/16T 3700x, 32GB DDR4 3600, B550 board, 1TB NVMe, RTX 3080, 750W PSU, very good 240mm AIO CPU cooler, airflow focused case.
Things you can easily reuse though:
Power Supply: EVGA SuperNOVA 550 GS
It's 650W, if I'm not mistaken. Should be fine for a 3080 and 3700x. Especially if you don't plan to do crazy overclock.
2x Crucial MX300 750GB SATA 2.5 Inch Internal Solid State Drive - CT750MX300SSD1
Even if you buy new drive. There is no reason why you shouldn't reuse those two.
Memory:
Patriot Viper Elite PVE48G266C5KBL Extreme Performance 8GB (2 x 4GB) DDR4 Kit PC4-21300 (2666MHZ) Blue
Patriot Viper Elite Series DDR4 8GB (2x4GB) 2666MHz PC4-21300 Dual Channel Kit (Black/Grey)
Running even faster memory on Ryzen and Intel systems will boost CPU performance in CPU "critical" situations. It's not necessary though
CPU Fan: ARCTIC COOLING Freezer i32
If you have a mounting kit for AM4, sure reuse it if you want.
Case:
Phanteks Eclipse Series P400S Silent Edition, Steel ATX Mid Tower Case Satin Black PH-EC416PSC_BK
I'm not a big fan of that particular case, because it is rather bad in the temperatures and airflow department. But it is modern and if you like it for other reasons, nothing "wrong" with it.
Things you want to upgrade:
CPU:
Intel Core i5-6600K 6M Skylake Quad-Core 3.5 GHz
Motherboard:
MSI Z170-A PRO LGA 1151 Intel Z170 SATA 6Gb/s USB 3.1 ATX
Video card:
MSI GeForce GTX 1060 DirectX 12 GTX 1060 GAMING X 6G 6GB