Agree. He should leave the club now, he is already 29 years old.
However, it is better to choose a stronger & established club if he wants to win trophies easier. Man United isn't an ideal place to move, I'm sure Bayern Munich or Real Madrid is the most ideal destination.
It's hard for him actually. Spurs is his club which played major role building his career and what he stands today so it is very difficult to part away from Spurs. Yes, its been difficult period for the club and the player but its a very difficult decision to make.
Manchester United is also not a bad option but yeah it can affect chances of other players like Martial. Bayern is also a good option but Madrid I have my doubts as they have Benzema already and they might not go for a second option which will cost them over 100m.
2. Dusan vlahovic > Bayern/ Arsenal
Nah we don't need him. We already have some really great players playing in that position like you mentioned and I don't think we need some more. Remember we also have Balogun who has scored 18 goals in Ligue 1 for Reims. It will be good for Bayern though since they need a striker apparently.