A lot of people build personal deep learning machines. The economics and convenience can definitely work out... I am confused however by "dummy GPU" - I searched for "dummy" for an explanation but didn't find one. Modern motherboards all include an integrated video card, so I'm not sure what this would be for?
My personal DL machine has a 24 core CPU, 128GB RAM and 2 x 3060 GPUs and 2 x 2TB NVMe drives in a RAID 1 array. I <3 it.