I don't particularly agree on Gueye or Hart mate but FWIW think you're right about the midfielder.
For me, Barry will do the job fine if we're playing a counter-attacking system. As long as he's managed right in his game time he'll be brilliant for us this year IMO.
However, I personally still think we need a player who can dominate a game from deep - especially against teams that we should be beating comfortably on paper.
That being said, if we sign Ghezzal, then it appears Koeman (who has publicly stated he wants Ross to take more responsibility) may well choose to move Ross deeper - either in a 2 or as part of a 4-1-4-1/4-3-3.
He won't keep the same formation for a lot of games and I think that will benefit us. So it may well be that signing another player who can fill a role up top means that Barkley can take on that role of a box-to-box player.