Memory: Well, that mostly depends on your input-data. To process reasonable sized pages, about 300K of free ram should be enough. For large pages and projects using loads of documents, this can increase to 1MB or even more.
Stack: A stack value of 8K usually should be sufficient; at least, this works for these documents.
AmigaOS and CPU: Basically, it works on an A2000 with AmigaOS 2.04 and a plain 68000, but it won't be much fun for you. As hsc is not one of the fastest, a CPU >=68030/25MHz is recommended.
Any other OS hsc is known to work with requires more hardware to boot the machine then hsc will ever be abel to request.
hsc is not a tool for beginners. It does not make html easier. It only makes it a bit less painful and brain-damaged - that's all. There exists several sources for beginners, and this won't be page #1876545 which lists these sources (But I'm frightened, the section about related stuff has degenerated to one of these pages..).
As hsc is a CLI-only-tool, any knownledge how to work with mouse and icons is not required.
If you utilize the project managment capabilities of hsc, you should know how to cope with make and Makefiles.