This is the closest I could get for your budget.
RAM: This RAM is on the QVL. It takes a long time to find QVL memory. I'd suggest taking the time and pouring through the QVL for the motherboard to find 3000Mhz or 3200Mhz QVL memory. If not this 2666Mhz set should work according to the QVL.
RAID: The motherboard has built in RAID 0,1,10 support. If you want a dedicated card. You'll need to budget more or drop some requirements. There is always Storage Spaces in Windows 10 Pro if you want parity.
GPU: Went with blower style. I prefer that in a multi-GPU stack. Recirculating fans struggle when they have little air space between cards. The blower style have a high static pressure and directly exhaust warm air.
Case: Just a basic big case.
SSD: Wasn't sure if you wanted top of the line or not. Figured you would and used the Samsung 970 Evo. You can always save some money with an SATA SSD.
CPU: Latest 2nd Gen threadripper 16-core. You don't have the budget for Epyc. Definitely not for a Xeon of this level.
Motherboard: May need a BIOS update before the CPU will work. It supports BIOS Flashback. So, you should be able to update with a USB Flash drive when no CPU or RAM is installed. If you don't want to deal with this. Get a first generation Threadripper.
PSU: High quality unit should handle all the load those cards can deliver plus a heavy CPU overclock.
CPU Cooler: Just a general high end 280mm unit.
PCPartPicker part list /
Price breakdown by merchant
CPU: AMD - Threadripper 2950X 3.5GHz 16-Core Processor ($898.99 @ SuperBiiz)
CPU Cooler: Corsair - H115i PRO 55.4 CFM Liquid CPU Cooler ($139.99 @ Amazon)
Motherboard: Asus - ROG Strix X399-E Gaming EATX TR4 Motherboard ($328.99 @ B&H)
Memory: Kingston - HyperX Fury 64GB (4 x 16GB) DDR4-2666 Memory ($680.60 @ Newegg Marketplace)
Storage: Samsung - 970 Evo 1.0TB M.2-2280 Solid State Drive ($297.99 @ Amazon)
Video Card: Asus - GeForce GTX 1080 Ti 11GB Turbo Video Card (2-Way SLI) ($689.40 @ Newegg)
Video Card: Asus - GeForce GTX 1080 Ti 11GB Turbo Video Card (2-Way SLI) ($689.40 @ Newegg)
Case: Phanteks - Enthoo Pro ATX Full Tower Case ($99.99 @ Newegg Business)
Power Supply: EVGA - SuperNOVA P2 1200W 80+ Platinum Certified Fully-Modular ATX Power Supply ($169.89 @ OutletPC)
Optical Drive: Asus - DRW-24B1ST/BLK/B/AS DVD/CD Writer ($21.30 @ OutletPC)
Total: $4016.54
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2018-09-17 15:08 EDT-0400
Edit: To get everything you want with Xeon or Epic plus workstation components. You are probably looking at a $6,000 to $7,000 budget. Even more, by a wide margin, if you want true workstation GPU (nVidia Quadro).
If you are using Windows. I would suggest Windows 10 Pro. If only for Group Policy. So, you can disable updates. As you don't want a reboot happening when you are working. There isn't any compelling need for the Windows 10 Workstation version. It's for much heavier duty computers.