I was dualbooting 2 Linuxes for a long time. All that you need is to install GRUB once on one of the distros, but having two or more bootloaders in the same EFI System partition is generally harmless, and might happen due to how some distros’ installers are written. In that case the BIOS boot order will decide which one to use. Either way, you only need one boot partition.
It is safe to delete all partitions on your hard drive if and only if you have backed up any important data on them. It’s basically the same as installing a new hard drive. The installer for your distro will be able to re-create all of them.
I have personally never used a shared /home between multiple distros, but based on my experience switching desktop environments, there are likely to be conflicts between files that lead to bugs. Arch and Pop!_OS will have vastly different versions of most software, and it’s possible that changes to a config file in one distro may break the program in the other. Shared /home is better for if you have just one OS installed, and reinstall it occasionally.