Strange to see no Blackmagic cameras.
Take a look at the hight of the audio monitors. At this workstation giraffes are doing the job.
You can DIY for around 240 U$ with Intel 660p for around 194 U$ and an USB-C - PCIe-NVMe-M.2-Enclosure for 45U$. You will reach the same speed. I used one from Icy Box https://images-na.ssl-images-amazon.com/images/I/71zR9qhSdfL._SL1500_.jpg, but there are many others.
Take a look at where the audio-monitors are placed. Either you are as tall as a 'avatar' or you have no idea about audio-monitor-placement.
compresso, the software for coffee adicts ...
This is very easy to answer. The Nvidia GT 750M offers 2GB of VRAM, the new macbook pro can be configured with 4GB of VRAM. For Resolve and 4k nothing but the maximum will satisfy you.