Depends on your formation.
You NEED a left winger. Daniel Halfar is great there, over 80 assists in 3 years for me. Buttner is good backup for both LB and LW, so don't sell him. Also, he's HG for Europe. For backup and future, look at Kishna from Ajax and Lenny Nangis. If they don't want to join, search for Stefan Babovic.
Just like on left side, you need a backup for Chanturia. I would suggest to take a look at Barazite, should be available for 4m. You can use Jenner or Hofs as right wingers, they were solid for me first season.
Central mids, hmm... Ruben Jenssen wants to join, but he'll ask like 20k pw salary. Price, 4-5m. Guido Pizarro is great and has good PA, he's available for 2m. For DMC either Salami or Kara. Maybe even Adam Voss.
CB's, you have Kaisha whos good enough, you just need one more. Mat Cahias is good, Anderson Marques is solid..
I sold both LB and RB at January. Got myself Gabriel Silva and Mattias Johansson ( highly recommended!). Great job. Later, you can buy Anita for LB.
Don't mess with GK's, you gave great keeper. Velthuizen is national squad quality, and you don't really need better backup GK than Room.