You shouldn't need to worry much about kernel modules nowadays. If you need, then you will notice
About Grub, well, it lives in your MBR usually, so you don't need to install it again, but you will need to know how it works and setup it correctly so it can find the kernels for all your distros. Sharing /boot can sometimes help with that. I find that kind of setup easier to maintain myself, but I guess it's a matter of personal preference.
Sharing /home is not difficult if you plan to use two non-matching user accounts, one for each distro. Using the same $HOME with the same UID is another matter, because different program versions will break the config files every once in a while. That's specially true if you will be using two different kde versions (even if only slightly different) across distros.