bob, to answer your questions no.
if you only make one partition everything will be overwritten with a new install of a different distro. same with the grub.
debian uses grub by defauit, so if you know how to play with it, you can configure it before you reboot and run.
make a cp of all the important things in your home. drop them onto a disk, cd. then just cp them back to your new home, chown -R bob:bob /home/bob , that will take care of it for you.