AmigaOS has a 4GB limit.
And 4MB RAM will be very tight with large harddrives. Is this 4MB Fast RAM, giving 6MB RAM in total, or 2MB Chip + 2MB Fast, giving 4MB total?
With only 2 MB Fast RAM you should not go beyond the built-in limits. Every additionally loaded driver will eat a little RAM and drive buffers will eat the rest.