Concerns like this seem to be normal especially when looking at Chelsea's performance this season especially with the majority of players in attack and midfield now new and the coach also new will certainly give concerns about the chemistry that is woven.
It would be great if Pochettino could get his squad right and not face any problems with adaptation but this is the Premier League and sometimes the season can be much harder than expected. Even though Pochettino has more knowledge because he has been at Tottenham before but this is also not a guarantee so it is quite natural when there are many concerns especially for fans from Chelsea who hope that their bad condition this season will not be repeated next season.
I hope the new deal that are coming to Chelsea are worth it and his decision on selling the previous men are rely worth the move he made, I don't have any observations about his ability but his record and experience is a great concern but perhaps the board director were willing to let that aspect slide for the moment. However, letting go and selling half the squad of a team is a thing to be priorize and look over again, he should have only sell when Chelsea potential bid are coming, not like he doesn't have any budget to buy, as they coming in and selling out, balancing the sheet is wouldn't be a hard job to do but what do I know, he is the man for the job but I can see a history of any English trophy in his resume, I just hope this moves should be worth it in the end.