Pertaining to my 1988 190e 2.3 8v without ABS .

I rebuilt my calipers, installed new Brembo discs front and rear, new pads front and rear (oem), new lines, new hoses, and new brake fluid Pentosin Dot 4.

The problem is that I have to use a lot of pressure to stop the car. What can I do to check my system? Also, I'm wondering how I can know if my power brake booster is functioning properly and if master cylinder needs to be rebuilt or not. Another thing that I'm wondering is if there is air in the hydraulic system, could that be thew reason why I'm experiencing this problem.

Thanks in advance.