Power train Khorasani, Boukherta and Reichor. Leave the others as they will be 4* and less next season.

So dedicate 50 rest packs for each player = 150 rest packs needed. Of course if you buy new 5* players next season then power train the young, fast trainers and dedicate an additional 50 rest packs per player. You will end up spending a shed load of tokens but it's value for money in the long run