Regarding (2) I’ve used Filen and it does look promising - I would recommend having your own offline backup of anything you store there just in case. When it comes to photos, I’d recommend Ente because it has a great user experience specifically for photos. Especially when it comes to sharing albums with people you can quickly create links, and even use those links to allow others to upload photos if you were out with family/friends.
Generally speaking, I view photos as something that’s better kept in their own place. For example, if I used iCloud Drive for cloud storage, I wouldn’t recommend also putting photos in iCloud Photos.