Hi,
For starters, try finfind answers to your questions, it'll save you
time. Most of what you asked can be answered by browsing around
debian.org, the list archives or searching.
As for versions, i'd stick with stable. Personally i use unstable for
desktops but it does have its occasional quirks (X not starting up
being one of them).
Contribution is up to you, i don't call the shots but tend to think
the best way to contribute is to report bugs.
For your hard-drive setup, read about LVM and/or RAID, i think that's
what you want.
The installation can be done from different media; CDs, flash drives,
through bootp, minimal net install...
The debian site has an installation manual that'll keep you busy for
hours. If it seems daunting, try installing Debian on a virtual
machine in Ubuntu first. Easier to clean up a mess.
HTH,
Nuno