ErA.l

It's fine. As long as you are not overclocking.

I usually use Macrium Reflect's free version. Has worked for me so far.

CPU: AMD Ryzen 7 3700X 3.6 GHz 8-Core Processor  (£269.00 @ Amazon UK) 
CPU Cooler: NZXT Kraken X63 98.17 CFM Liquid CPU Cooler  (£119.99 @ Box Limited) 
Motherboard: Asus ROG Strix X570-F Gaming ATX AM4 Motherboard  (£234.99 @ AWD-IT) 
Memory: Crucial Ballistix RGB 16 GB (2 x 8 GB) DDR4-3600 Memory  (£89.99 @ Amazon UK) 
Storage: Crucial P1 1 TB M.2-2280 NVME Solid State Drive  (£101.18 @ Amazon UK) 
Storage: Toshiba X300 4 TB 3.5" 7200RPM Internal Hard Drive  (£92.98 @ Laptops Direct) 
Case: Lian Li PC-O11 Dynamic ATX Full Tower Case  (£114.95 @ Box Limited) 
Power Supply: SeaSonic FOCUS 650 W 80+ Gold Certified Fully Modular ATX Power Supply  (£95.47 @ Scan.co.uk) 
Total: £1118.55
 

I'd go with the crucial P1 (or similar) nvme if I was you, along with the faster memory. 
 
 
 

For Ryzen Zen2 I would recommend 3600mhz memory, pref with a CAS latency of 16.
 
That monitor is horribly overpriced too. 
 
What is your use case and budget?

There is a huge difference in cooling methodology between an iMac and a Mac Pro. The iMac runs a consumer CPU that is soldered to the board, and  the higher grade cpu's often has the boost clock artificially limited to prevent throttling due to insufficient cooling.
 
The Mac Pro runs a user upgradeable server grade cpu. The Mac pro has a pretty ingenious cooling system that runs 3 giant 20cm fans that are acoustically optimized and ducted though a proprietary stacked fin heatsink. The Mac pro's cpu is in no way limited, running at the standard Xeon specs as indicated by the CPU. And while it has great acoustic properties, a high spec CPU running under sustained load will produce an audible fan noise.

Depends on how much Solidworks you will be doing. The 3900x will definitely be better if you are going to be doing a lot of CAD rendering. If you only do it rarely, i'd save the money and get a 3700x.
 
For the 3900x one should consider aftermarket coolers if you are looking at overclocking or sustained loads for rendering and video encoding. I'm not sure why you think watercooling is worse for sustained loads, but a decent aircooler like the Noctua nh-d15 chromax black or Darkrock Pro 4 will probably be about the same 240 aio. If going Noctua, also look at some white Chromax accessories for the Chromax black cooler.

He had a 500w listed and wanted an upgrade path. A 3950x with a 2080ti can pull rather more than 500w. So I'd go with a 600w minimum for efficiency headroom.
But that's just me.

Yep, for me probably too, but its dealers choice:
3700x & 2080 Super = Gaming Build
3900x & 2070 Super = Productivity Build

My pick would be:
CPU: AMD Ryzen 9 3900X 3.8 GHz 12-Core Processor  ($848.00 @ Shopping Express) 
CPU Cooler: Corsair H100i PRO 75 CFM Liquid CPU Cooler  ($177.00 @ Skycomp Technology) 
Motherboard: Asus PRIME X570-P ATX AM4 Motherboard  ($289.00 @ Shopping Express) 
Memory: G.Skill Ripjaws V 32 GB (2 x 16 GB) DDR4-3600 Memory  ($302.50 @ Newegg Australia) 
Storage: Crucial P1 500 GB M.2-2280 NVME Solid State Drive  ($125.00 @ Shopping Express) 
Storage: Seagate Barracuda Compute 2 TB 3.5" 7200RPM Internal Hard Drive  ($89.00 @ Computer Alliance) 
Video Card: Gigabyte GeForce RTX 2080 SUPER 8 GB GAMING OC Video Card  ($1239.00 @ Centre Com) 
Case: NZXT H510 ATX Mid Tower Case  ($130.90 @ Newegg Australia) 
Power Supply: Corsair RM (2019) 750 W 80+ Gold Certified Fully Modular ATX Power Supply  ($179.00 @ Centre Com) 
Total: $3379.40
 
A bit over budget, to get some savings one could either drop the CPU to a 3700x (gaming setup) or the GPU to a 2070 SUPER (productivity setup) 
I put in the aio because that would be nice if going with the 3900x, but an air cooler can be substituted if preferred. 

PCPartPicker Part List
CPU: AMD Ryzen 7 3700X 3.6 GHz 8-Core Processor  ($298.99 @ B&H) 
Motherboard: MSI B450 TOMAHAWK MAX ATX AM4 Motherboard  ($114.99 @ Newegg) 
Memory: G.Skill Ripjaws V 16 GB (2 x 8 GB) DDR4-3600 Memory  ($83.99 @ Newegg) 
Storage: Crucial P1 500 GB M.2-2280 NVME Solid State Drive  ($69.95 @ Adorama) 
Storage: Seagate Barracuda Compute 2 TB 3.5" 7200RPM Internal Hard Drive  ($54.98 @ Newegg) 
Video Card: Gigabyte GeForce RTX 2070 SUPER 8 GB WINDFORCE OC 3X Video Card  ($489.99 @ Newegg) 
Case: Phanteks ECLIPSE P350X ATX Mid Tower Case  ($69.99 @ Newegg) 
Power Supply: EVGA SuperNOVA GA 650 W 80+ Gold Certified Fully Modular ATX Power Supply  ($76.98 @ Newegg) 
Total: $1259.86
Prices include shipping, taxes, and discounts when available
 
 
That leaves enough in the bank for a nice aio if are inclined that way. Or spend the $150 on a different upgrade
 
Also, double check if you really like that case. The looks and RGB is nice, but you will need to buy some extra fans (it only comes with one) , and it doesn't have front usb-c

PCPartPicker Part List
CPU: AMD Ryzen 9 3900X 3.8 GHz 12-Core Processor  ($418.89 @ B&H) 
CPU Cooler: Corsair H100i RGB PLATINUM SE 63 CFM Liquid CPU Cooler  ($155.99 @ Newegg) 
Motherboard: Asus PRIME X570-P ATX AM4 Motherboard  ($147.00 @ B&H) 
Memory: Crucial Ballistix RGB 32 GB (2 x 16 GB) DDR4-3600 Memory  ($193.99 @ B&H) 
Video Card: Gigabyte GeForce RTX 2070 SUPER 8 GB Gaming OC 3X Video Card  ($539.99 @ Newegg) 
Total: $1455.86
 
 
Add some nice custom cables, rgb fans, etc, and you'd have pretty sweet system. Video Card is totally subjective BTW. Chose that one cause its white
The RAM sticks should be available as 4x 8gb as well, but pc partpicker could only find stock of 2x16gb
 
so, black & white board, white rgb ram, white aio cooler & white GPU. Should look pretty fancy  needs some white cables.

3700x will be great for gaming. 
 
Some changes I'd consider :
 
Motherboard: Asus TUF B450M-PRO GAMING Micro ATX AM4 Motherboard  ($94.99 @ Newegg) 
Memory: G.Skill Ripjaws V 16 GB (2 x 8 GB) DDR4-3600 Memory  ($83.99 @ Newegg) 
Storage: Crucial P1 500 GB M.2-2280 NVME Solid State Drive  ($69.95 @ Adorama) 
Storage: Seagate Barracuda Compute 2 TB 3.5" 7200RPM Internal Hard Drive  ($54.98 @ Newegg) 
 
No RGB here, not sure whether that is important to you 

That is a "closed loop cooler", it comes pre-filled. No need to do anything to it, it should be ready to go out the box.
 
The motherboard is ATX, and the case is ATX compatible, so everything should fit fine.