If Dossena and Degan are to be sold (which I expect), with Aurelio injured a lot and Insua a little inexperienced then I see the signing of Johnson as a sensible one. He could come in an Arbeloa move across to LB. We'd then have Carra as cover for both RB and LB if need be.
That would then leave 4 quality CB's fighting for 2 places.
We need competition for places and also plenty of cover if we are to challenge for the EPL, CL and FA Cup. Look at yesterday...we could potentially lose Xabi and Mascha for a while and we'll need Lucas etc in the coming weeks.
It is difficult to keep all players happy but I trust Rafa's judgement and management skills to keep everyone happy.