using FreeBSD to create a completely new OS

[Aryeh Friedman]

For personal hobby reasons I want to write an OS completely from
scratch (due to some aspects of the design no existing OS is a
suitable starting place)... what I mean is I want to start with the
MBR (boot0) and go on from there... I only have one *REAL* machine to
work with which means I need to work with something like
emulators/virtualbox-ose... I also want to do as many automated tests
as possible (for example seeing if the installer copied the MBR [and
later other stuff] correctly to the virtual HDD).... for this reason I
have a few questions on vb (or perhaps QEMU if not possible in vb):

1. Can it be scripted?
2. Is there any documentation on the various virtual HDD formats and
such (that way I can check the "physical" drive and not by indirect
query)?

Also can people give me some idea of a good general
development/testing framework.... the one I have in mind so far is:

1. Write enough of the OS in FreeBSD to boot and give a command prompt
and then develop using it (assume that there is a working compilor
[note I am doing it completely in Java (note 1) and will be using
either gjava (gcc) or writing my own compiler])

Notes:

1. Due to OS's needing to address physical RAM directly (DMA mapped
I/O) I will be introducing some form of ptr's into java with the
compiler or native ASM