I think that the transfer window closes this year before the season starts.
There is also a major competition in the summer and a lot of players will want their futures sorted before they leave so they can put the uncertainty about their next season out of their mind.
I think transfers will be happening very early with quite a few being leaked ever before the season finishes.
I absolutely agree with you that if Sam is not staying then it has to happen early and his replacement be ready to step straight in immediately.
Realistically, a new manager should be looking at Everton and it's players now and trying to determine what is needed and who is available.
Sacking Sam in the middle of May and not appointing a new manager for even two or three weeks could be a disaster.
However, I am convinced Sam will be at the club next season and in time it would not surprise me if he becomes general manager as a new younger coach is brought to the club... it is in a scenario like this I could see Silva arrive.
An exciting young coach working under the umbrella of a more senior man who will keep the club stable.