If you were planning on playing 3 at the back, you'd want two centre halves who are quick, athletic, and absolutely mustard on the ball. Stones and Laporte are all of those things.
Ideally you'd also want one to be left footed and one to be right footed. Lapprte is left footed, Stones right.
Then you'd want someone experienced in the middle to organise, a leader, a talker. Let's hope Kompany can get himself fit.
Playing 3 at the back is something Pep has done previously in order to squueze in an extra attacking midfielder.
Buying these two centre halves might just be part of his plan to squeeze Gundogan, Silva, DeBruyne, Sterling, Sane, Aubamayeng and Aguero in to the same starting line up. There could be plenty of 6-5s next year! :-)
This against Burnley at home would be a right laugh! :-)
.......................Hart
....Stones.......Kompany........Laporte
...................Gundogan
Sane.......KBD............Silva.......Sterling
...........Aguero........Aubameyang