I'm not sure about Carra. Players resented Thommo's shouty aggression and that was well over a decade ago. Unless Carra was much more controlled than he was as a player, and picked his fights very, very carefully, he'd probably end up like Keane at Villa. For better or worse (it's worse, obviously) most young players these days resent any kind of criticism and just sulk if it keeps on being aimed at them. Besides which, as has been said, Carra is content at Sky and probably won't ever go back to the game in an active role.
Sami might be too far in the opposite direction. I bet his stare is unpleasant but I'm never convinced he's a great communicator. Having said that, he might well be a subtly authoritative presence, and the bonus would be he'd know Can inside and out and would be an ideal mentor to him as he begins his development as a future leader of the team.
My wish list would be:
1. Bellers, because he's seriously working to be a coach, is articulate, still well-known to the players and would really push them at Melwood.
2. Barnes, because he should be at the club in some capacity, he'd be an inspiration to the likes of Sturridge, Ibe, Sinclair and Ojo, he'd shut Sterling up in an instant, he'd be an articulate figure who could take some PR pressure off Rodgers and he'd certainly have ideas in the dug out.
3. Danny Murphy, because he's bright, keen too coach and he'd be a tactful but articulate advisor behind the scenes.