This is what I reckon. Our new RB, whoever he is, will be the number one - and Harding, with his effort and good footballing brain, could be the back up right back - he's already proved he can play well there.
As for left backs, we're ok now, we've got Harding, Mills, and now Dickson (if we have actually signed him), plus a left footed Seaborne can play there if needed.
If it were me, and I'm not saying Pards won't do this, but I'd bring in a new quality right back AND a player that can play both at RB and CB - like Thomas.