The amount of SSD or HDD storage you need for 4K video editing will rely on the type of codecs you are working with.
Surprisingly 4K footage can be very small files. In fact, HD footage can be a larger file than 4K.
The key element is finding the bitrate of the file. You can do this on any Mac or Windows workstation by looking at the properties of the file.
Once you have the bitrate you can use the calculation below to establish how many GB per minute, which I think is the most useful information figuring out how much storage you need.
Kbps / 140000 = GB per minute
Mbps / 136 = GB per minute
Now there are lots of blogs that go into detail on the idea behind those numbers. But those are the quick calculations.
Once you have the GB per minute, it should be easy to estimate your storage needs.