As for the separate OSes and their software/data, that is not exactly possible. You can have separate partitions for each OS, their software and their data, but they will be visible. Even in OS 9 and OSX, they are still visible and accessible to each other.
The only thing I can think of is three partitions - 1 for System 7 on HSF, its software and data; 1 small partition for OS 8 Booting on HSF and 1 for OS8 software and data under HSF+. This would only hide the HSF+ partition from System 7, but everything done on System 7 can be seen in OS 8. This is not exactly a two-way street.