1. Buy the RAM yourself to avoid Apple Tax™, so stick with 8GB
2. Consider whether you need the matte screen, personally I'd highly recommend it for design work, so spring the $500
3. Max the GPU out if you're using Adobe CC
4. Get the i7 model if you need to save $400 cash, or the i9 model if you need this machine to last 4-5 years or so.
5. Skip the 10Gbps ethernet unless you do local data management with a NAS
6. Stick with the 512GB SSD and use a thunderbolt 3 or USB 3.1/2 external drive velcro'd to the back of the machine for additional storage.
Should come in around $4000 or less, definitely not $9000
This advice.
Even buying the entry model would be good enough. 6 cores, multi-threaded.
Buying the top tier at £2300 would make a great design machine. For a great value.
5k screen.
8 cores.
5500XT.
What more do you want?
Azrael.