Linux only, SSH works fine. Not e2ee. Nextcloud works fine but extra work unless you use a service provider. It can be e2ee but not normally so. Syncthing worth a look too. It is not cloud storage, but direct device transfer. Bitwarden send is useful too if you want to juat send file someone, and thunderbird is working on thunderbird send which might be interesting.
Maybe Synology if you want your own lan NAS?
Actually the safest thing is probably to choose a main system and run the other in a VM like with VirtualBox. For you, you could just install VirtualBox on Windows then Linux inside of a VirtualBox VM. Windows does have a builtin Virtualization solution too you may be able to use, but I have personally never done that. Keep in mind too that VMs are not as performant as bare metal. For video probably NO, for images fine, for audio maybe but you’ll have to see if you get the real-time timing you need in a VM. Good way to play in any case. 2nd best if you have a workstation, not a laptop, you could put in a hot mount SATA drive enclosure, and just swap in the drive you want and get full bear metal performance. Dual boot takes some tech skill. Be sure to back everything up if you do that. Should do that anyway before fiddling. Also if you use bitlocker and secure boot make sure you have all your recovery keys and know how to work with your bios settings too.
Maybe I am missing something, not sure why you care about NTFS. If this is a separate computer you don’t really care about that, just the sharing protocol (SMB for example). If it is on the main box, then you’d probably convert this to Ext4 or something similar. No reason to stick with NTFS with Linux. There are a lot of great FS options on linux plus BTRFS, LVM, or RAID to if you want redundancy.
Regarding apps. The alternativeto site is great. Linux has a bunch of audio and photo software. If your a pro, you may not find any of it sufficient. Especially a lot of people cannot do without Photoshop. The common quoted photo programs are GIMP and Darktable. There are many other photo and image programs. Common audio program is Audacity. Again, there are many others. Looks like some handle vst but I have no personal experience.