the idea is interesting, but i want to tell u that sutch idea (compatibility with windows and unix) is very hard to implement, and big projects around this idea fallen down, so i suggest u to think about simpler project, i ll give u some reasons :
-Unix systems use posix standards which are not used by microsoft
-Windows is closed source and it s too hard to find official and free documentations
-Developping an OS = Developping a kernel ..... compatibility is another question.
for ur other questions :
if u want to developp an object oriented OS u must use C++ since C is not oriented object language, and C# needs a JIT compiler :p
and the best environement to develop an OS is Unix or Linux, not windows 2003 server :p
the best editor is VIM (and emacs for its fans
)
but i want u to explaint me something
why r u speaking about ur configuration ???