I think Morata is better than Costa if you ask me, Costas a good player, but he's not quite a 25 goal a season guy, I think Morata is. I think that 25 goal mark is what the very best strikers will consistantly get to if they don't have any injuries. I think if Morata stays fit he'll reach that. As you say Batshuayi isn't cut out to play from the start, so you better hope Morata stays fit.
That's where the positives end for me though, Bakayoko is definitely no upgrade on Matic. You need 2 holding players who are good at winning the ball back with the system you play. This is why Fabregas struggled for game time last season, as in a 2 man midfield he's to much of a luxury player. Bakayoko may be a big powerful lad, but he's not the defensive shield that Matic is, he will leave to many gaps in your midfield, especially against better teams.
Drinkwater plays the same role as Matic does, so I don't see how you could try to claim he isn't a direct replacement. For the same money you all know you'd rather Matic.