generally speaking, if you nominate an existing partition and format or not format it....the installer will overwrite it with its system files......note system files
therefore boot can not be appended but you could take images such as with www.partimage.org
which is what I do.
2) it does mean however that you could risk not formatting a separate home partition but I have never tried it.
3) your iso is a bootable cd image so as its not a hard drive image like a vmware file.....the grub is not the answer.
it looks to me that you are trying out a few distros?
so consider going for partimages which can be burnt to cdr or dvd media
maybe running Xen?