File access across systems is no problem.

It just has to be a separate partition either in the form of a whole SSD/HDD or as a partition on your main drive. Just make it NTFS (a file system that all those OSes know) it works with both windows and linux. I still have 3 NTFS partitions from my dual-boot days.

FWIW, I only needed to install one package to be able to read the drive that my Windows install is located on/a shared drive between my two installs. It has been very easy to access the Windows partition from my linux install, but I have not needed to access my linux partition from the Windows install yet, so can't speak to the ease of doing this.

Yeah, just make a drive/partition NTFS, and it will be usable by both systems. Please note that some Linux software doesn't work well with NTFS, for example Timeshift (backup utility) and Steam Proton, so it's best to have an ext4/btrfs drive for things you do exclusively on Linux and NTFS for common files of both systems (like documents, music, films, whatever)

I usually use USB sticks for sharing files between VM and host.