Hi there ,
Well even to exact copy the iMac Pro, it costs close to 3000 to 4000 USD comparing to Baseline iMac Pro, around 5000 USD. (Price in USD, but you get the idea). If you think of ECC DDR4 RAM, which normal consumers don't use. An Average consumer doesn't need ECC RAM. ECC RAM will of course cost a premium. In your case ECC could be good, but not a necessity. This alone costs 500 to 600 USD just for 32gb. Then the Server based motherboard, in iMac Pro's case, Apple uses a custom chipset made by Intel, close to C402 Intel Chipset, 500 USD again.This is a server based chipset, so for the use of Xeon CPU's with Socket 2066. And if no Xeon CPU, then there is no need for ECC RAM. A Xeon CPU for such system would be at 1000 USD range. And then the other essential bits, a gfx like Vega, maybe around 700 USD. etc. Now I am telling this to give an idea. Of course there is no need to Copy iMac pro 100%.
Keep in mind though, Apple MacOS is more optimised for Apple's own computers, that doesn't mean you cannot get a Hackintosh to work close to the same optimisation levels.
The content creation world relies a lot on the Open Libraries, such as OpenCL and OpenGL, Adobe use it, Apple uses it and even BlackMagic DaVinci Resolve uses it etc. Far less go towards utilising CUDA by Nvidia. Nowadays, people using Nvidia graphics cards for content creation do it more because of their comfortability, being already known to the hardware and its supportive utilisation methods. AMD Graphics Cards on the other hand, are more optimised for such stuff. That doesn't mean Nvidia is a bad purchase. But one should always read why what is good to use, and why one should use it over the other for their own needs. In your case, content creation. But every content creation type is different, people use different tools, software and even Operating Systems. You know better about what you use, and you know how you will use them. Always good to read about what you use and what is much more compatible for it, than the other choices.
However, it is easier to answer to why one should use AMD Graphics cards for Content Creation when using MacOS. MacOS is much more optimised with AMD GFX, and Intel iGFX, the drivers for them are also native. Modern Nvidia cards need third party drivers from MacOS, if one needs to gain proper acceleration. In this case there is more focus for AMD cards to be optimised for MacOS by Apple. And this is a documented fact.
I am telling you this, because I always find it weird when people ask for hardware recommendation for specific stuff such as content creation. As it depends on your use and how you use the computer to do content creation, only you would know better.
You mentioned Apple Services (HandOff, iMessages etc.) was a must. For Apple Services, you would need to do some research, it is possible, but dependent on certain values that needs to be modified, edited or added, either in the SMBIOS section, or RT Variables for ROM and MLB and so on.
I agree with MaLd0n and Gigamaxx.
You would most likely be ok with Z370 CoffeeLake and 8700K 6-Core Processor. 64 Gb would be good enough, if 128 Gb is a must, then you would need to find a compatible board for it. An AMD Radeon RX card would most likely do the trick.For the SSD, you really don't need 1Tb SSDs as passive storage, you can use HDDs. Unless the SSDs are for heavy exportation work. I could understand that one would want thin non bulky and high storage capacity SSDs though. As a boot drive, just use NVMe SSD. It seems that anything is possible to Hackintosh lately, so this isn't a problem.