The specs seem okay for what you asked. I would recommend a 2TB SSD minimum. You very likely will end up wanting to do more with your server, and 1TB won’t be enough.
StartOS is developed, and tested specifically for servers we sell. Because it’s built on a Debian Linux base, StartOS works on most x86 devices, but not all. The DIY compatibility list is a list of machines reported working by users like you, and not tested by Start9. In short, if you want guaranteed compatibility, it’s best to buy a server sold by Start9. This supports the project, and also gets you lifetime live support. If you are willing to take a small risk, and deal with some minor incompatibility, choose a machine on the list that has been reported trouble free by another user. If you are willing to be the first one to try a Gookom A6, please report your findings for others. Just keep in mind that it may not work at all.