The footrests are very thin (~ 3 cm). When my daughter was very small, I 3D printed footrests for her. Now that she is bigger and wants to rest her feet, she stretches her legs forward.

Do you mean the white handle at the back? Yes, it can be removed, as well as the seat back and the side brackets. So it can be used on four sides.

There are 3 or 4 "songs". I didn't notice any connection when I mounted the handlebars. Have you already looked behind the big cover next to the battery?

No, they are normal hard plastic tyres

The assembly procedure is easy. You will only need a screwdriver that is not included in the box. You will also need 4 AA batteries to operate the sounds and lights.

There are no footrests, but it has side guards (2in1), various sounds and a horn.

Yes, both can be removed. Instead of the handlebars, it has an attachment so that the child can push the car well by itself.