With that much RAM, you don't need any SWAP partition. If you have plenty of disk space then create 1GB SWAP partition. I am sure it will never be used though.
GRUB is one of the simplest and easy to manage boot loader. You should not worry about GRUB or multibooting. Leave it to the installer.
Just install distros of your choice and let installer install GRUB in its default location. As nujinini mentioned already, GRUB of last distro will take charge of multibooting automatically. You don't have to do anything special for that. It default in all Linux distros except RedHat based distros like RHEL, Fedora and CentOS.