Tigger Idoc for Goods Movement

Hello,

I need to confirm few points on Outbound trigger of Idoc for GR or Goods movement(MIGO).

1) There is no standard thing availlable for it. Mean to say we need to create custom Output types, Functional Modules and Programs.

2) Trigger point should be Posting of material document. Wanted to confirm that whethere this will be fine or trigger should be something else(consdering performance issue)

3) Is MB90 can be used to send outbound Idocs?

Regards

Himanshu