Might be my age, but Casper is a friendly ghost to me! In my generation it would be laying them open to being teased for it (especially if he's likely to be blonde or fair skinned) but if its known as a regular name for kids now then go for it. Its nice enough, just my associations.
Don't love Franklin, it's very American for me. And as a PP said, will end up as Frank.
If you like some of the older names that are coming back (which I love, but admit was really suprised by the first little baby Arthur I met some years ago🤣)
Alfred
Samuel
Henry/Harry
George
Frederick/Fred
Patrick
Graham