How to create a component list for Purchased items and easy way for make items

Hi All We have the following business scenarios:

1. Machines that are made in house and some machines that are made by a contract manufacturer that we purchase as completed machines.  These are all serial tracked IB items

2. Both these types of machine have components that are IB serial tracked

The general structure is

Item ABCD Serial number 123000

->component EFGH number 124000

->component IJKL number 125000

I have two questions:

1. What is the best way to add the components for the internal make items to create IB component List.  We are using WIP but we need to control which component serial number goes to which end item serial.  If we set the IB WIP install flag id just auto allocates which we do not want to do.