The only issue with the Witcher's setting is the current party composition.
The setting is medium on the magic scale, and only one of our characters isn't a full caster.
I would create a new character for the Witcher setting, as Changelings do not exist in it.
Player races would be limited greatly as well: Human, Elf, Half-Elf, Dwarf, Gnome and Halfling are about the extent of the basic player races in the setting. Some other races I can allow, but are extremely rare.
The setting is also very gritty.