Update on Caramel - she seems to have settled in well and is now really pretty tame. We've dispensed with the playpen and we play with her on the sofa like our other hamsters - she'll happily climb all over us and, though she won't willingly walk on our hands (never-ending stairs etc), she seems happy enough being scooped up. She's happy being brushed lightly with a baby hairbrush and will take food from us confidently.
Her bar chewing is a problem though - I'm going to try and rectify this over the weekend