MS-DOS can run on any memory configuration and any HD configuration (except SATA), you will just be unable to create partitions larger then 2GB due to the limitations of FAT16.
Since DOS itself only uses the 640K of conventional and perhaps some of the HMA, the amount of RAM installed is completely dependent on the other applications one wishes to run. For example, Windows 3.1 can use up to 512MB of RAM(I believe some may not be detected actually), which means that the limitations become purely based in it's lack of "selectors" or handles into that memory.
Squall- WHY do you insist on low-level formatting? It erases all the Servo information about bad sectors and so forth, which means your OS will need to "rediscover" the bad sectors. Unless of course your not really low level formatting.
I really love your detail- "what's supposed to show up isn't" and yet you make no mention of either what is supposed to show up, what is showing up, OR the book your using.