If Spurs want to challenge for the title and more, I don’t think Grealish would take them there. He would be a decent player to offer them some depth though.
However, Pochettino may be able to work his magic on him and make him into a top talent like Ali, Son, Kane and son on, but that would take some time and is a huge gamble. If Eriken leaves Spurs should be going for players like Pepe, Suso or Chiesa. pochettino has made Spurs a contender for the title, so their board should start supporting him in such manner.
Beside those attacker, an elite midfielder. Kroos may leave madrid to make way for some of their signing. I feel that he might do well at Spurs if Eriksen leaves and provide great range of passing. However, Pochettino seems to like strong hard working midfielder, so N’Dombele would suit your side more.
Lloris/Vorm
Trippier/Aurier - Alderweild/Sanchez - Verthgonen/Forsyth - Rose/Davis
Sissoko/Wanyama - N’Dombele/Wink
Eriksen/Lamela - Ali/Grelish - Son/Moura
Kane/Wilson
*Eriksen leaves a player like Suso, Pepe, Cheisa, maybe even the return of bale.
**Alderweild leaves a player like maguire.
I feel this is the type of team or something similar will be able to take you to another level.