You will probably have about 375 GB of free space, maybe a little more. I have several apps installed, along with a couple of VMs. I am only using 200GB out of my 1TB. I don't store a lot of movies or pictures. I do have about 3K songs on the machine.
512 will probably suit you fine. If you need more space, get an external drive for storage. One from OWC, TB5, 1TB is not much more than the "Apple Tax" and will perform as well as internal storage.