Re: Neymar and how he would fit with CR7, I put something together comparing Neymar, Dybala, and CR7.
A few things are clear:
In a 4-3-3, Dybala is utter crap. Whether he plays wing or centrally, he has performed badly. Despite consensus here than Dybala played mostly as a CAM, in fact, he played more games last year as a CF in a 4-3-3 with Ronaldo. He also played a few games on the RW. He average .44 in total production in that formation. Ronaldo and Neymar can both play in a central role or in a wide role of a 4-3-3, and put up fairly similar. Neymar as a false 9 in Barcelona put up an 6 goals and 3 assists in 5 games in that position when Messi was injured in 13/14. CR7 put up similar performance whether playing centrally or wide left.
In a front 2, Dybala thrives with .82 in production per game. This includes his times playing there this past season, the 4-2-3-1 of 2 years ago, but not that of 3 years ago because he played more like an AM since Mandzukic was on the LW. 2 years ago it was mostly actual wingers and he played closer to Higuain. CR7 & Neymar both produce at similar levels in a front 2, but Neymar scores more.
As an attacking mid, Neymar was very good but only played 3 games. Dybala is bad generally. He is better in a 4-2-3-1 because there are fewer attackers, but if he is playing behind 2 scorers, he basically doesn't produce at all.
2 Conclusions:
if by some miracle we actually do get Neymar, he will work with Cristiano. They can freely interchange between central and left positions, and both will be effective. With Dybala, it looks like we'd be better off with a 4-3-1-2 with Dybala as a striker. A 4-3-3 with Dybala playing centrally looks challenging unless Sarri's system can bring out something unseen before.