Suspension Problem

[shams13]

I drive a 04 E240 (non-airmatic) 120000 KM and feel some suspension problems;

1. When i get past a big hump, the front part of chassis hit the ground pretty hard. this happens when i have 3 or more passengers on board. Have my springs gone weak??

2. While coming out of a turn, my steering doesn't completely set back to the center by itself. i manually rotate almost 10 degrees to bring it back to the center.

3. i installed brand new tires, but have a vibration over 60KPH. Balanced those even with road force balancer but in vain. One technician suggested to change the Idler Arm. does it make sense??

please help