It makes a lot of sense to get former players involved at the club, in a well thought out structure after they got the necessary education. But who's part of the coaching staff should be the manager's decision. At Bayern, we always had Hermann Gerland around during our transition in the last 5 years, switching between youth coach and 2nd assistant coach in the first team (Van Gaal had Joncker as his primary assistant manager, Heynckes had Peter Hermann and Guardiola now has Domenec Torrent, who already was part of the coaching staff at Barca). Gerland was always a background figure (since 2001 at Bayern), who was important for the development of our youth players, he wasn't influential in terms of tactics, playing style or the club's philosophy. He was there to give his input about the players from our youth academy. That's helpful for the manager because he gets input, no one else could give, but the manager's authority can't ever be undermined. Most of the first team managers brought a big coaching staff with them. Guardiola wanted to use his own assistant coach, video analyst, physical therapist and a few more.
If the club hires van Gaal, it really should mean that there's a clear cut. Then Giggs, after being interim manager and after Ferguson's comments in public, could easily become a problem. He's too close to the players and I'm not sure what kind of assistance he could provide, if van Gaal changes the tactics, playing style and training methods. I'm sure if Giggs and/or Scholes want to make their coaching badges and coach on youth level, van Gaal wouldn't mind. Forcing the manager to take them into his coaching staff sounds like a horrible idea though, that would never happen at Bayern. Scholl never had any influence on the first team, he started coaching the u-13 while getting his badges and later took over our 2nd team.