I think he can be successful again, but this time things won't be as easy as before. In his career as a footballer, he faced tough tests under pressure, but I don't think his career as a manager has faced this yet...
Well, I don't think you can have enough preparation to manage a club like Madrid, where a trophy is expected every season. It's a tough task, but you have to start somewhere to be able to cope with it. Hopefull,y the management and the fans are not that impatient and treat him terribly (if he did join them), especially if he can't get the players that he wanted. There are many examples where a good manager failed to deliver because the environment didn't support them. Of course, there are exceptions like Klopp or Guardiola, where they can shape the environment to what they want instead. I think it's too soon to judge if Xabi dan do the same or not.
I don’t think Xabi Alonso has enough experience to be the head coach of Real Madrid. However, he is a player who is committed to the club. He was a player who loved Real Madrid very much and fought very well for Real Madrid in the past. Currently, he is a manager who experienced a magnificent championship with Bayer Leverkusen and is currently chasing the championship. Of course, his opportunities at Bayer Leverkusen are very limited and despite these limited opportunities, he has made him one of the most popular managers in Europe. I think that Real Madrid can provide better management and be successful with its unlimited opportunities, but we need to see this.