It kind of depends on your club's rep and budget - you can sign anyone for any role if you have enough rep and are prepared to pay.
That said, the following can usually be signed for top teams, don't cost the earth and are all 4.5 stars:
Assistant Manager and Tactics Coach - Francisco Ayesteran (use him for OIs as well)
Defending - Massimo Carrera
Attacking - Sergio Zanetti
Shooting - Fausto Salsano (can be hard to sign, Jeffery Talan is an alternative, 4 stars)
GK Shot Stopping - Alessandro Nista
GK Handling - Marco Onorati
Fitness Coaches (all 5 stars) - Valter di Salvo, Antonio Pintus, Gian Nicola Bisciotti, Antonio Bovenzi
Physio (or Head Physio) - Lieven Maesschalck
Head of Youth Development - Bernhard Peters
Youth team Manager - Norbert Elgert
Scout (or Chief Scout) - Luciano D'Onofrio