using FreeBSD to create a completely new OS

[Perry Hutchison]

> ... a special arrangement that allows me to skip
> the course work part of grad school ...

[shudder]

I hope that "special arrangement" includes passing the final exams,
or otherwise demonstrating that you already know the content, of at
least the minimum course work that would ordinarily be required :)

> [I have not formally started yet]

So you don't yet have a formally-assigned advisor :(

I hope you at least have had some substantial (although necessarily
informal) discussions with the department head, and/or the professor
whom you anticipate will be your advisor, before doing a lot of work
that might turn out not to be useful in your pursuit.

> I do not plan to do the whole OS just the stuff up to mid-level I/O
> (for FreeBSD this is also known as user land I/O)

While the userland is by far the _largest_ part, the low-level kernel
is likely to be the _trickiest_ part to get right ;)

Another OS for your research list:  Mach (which had been around for
a while before being adopted as the basis of Darwin, the MacOS X
kernel).  Darwin is highly modular; depending on what you're doing,
you may be able to write less code from scratch by reusing or
adapting some parts of it.