I'm thinking that if you do not specify a location for "/home" during the install process, it will install "/home" in the same partition as your "/" by default. Going this route would afford less chance of something getting messed up between the install "/home" and your Ubuntu "/home".
After you have gone through the installation, you could merely edit your fstab file to point to your Ubuntu "/home", reboot and see if all is happy (recommend just commenting out the installed "/home" line in your fstab for this effort). If all is happy, you're good to go. If not, change your fstab and use something like Krusader to copy pertinent settings from the Ubuntu to your new /home.
As always in the world of Lx, just one of many approaches to the same problem....
Linux'd since 2005 Linux ID 422356 Ubuntu ID 15015