A formal approval of the hardware and software suppliers is not necessary. However, it has to be ensured that orders are placed only with suppliers that have before been assessed and accepted.
How detailed do specifications have to be?
Specifications always define the desired quality. Therefore, they have to describe the requirements so that they can be used as the basis for the tests. Thus, they have to be testable, i.e. the customer should be able to test whether he has received what he had ordered. For commercial reasons alone the customer will describe in sufficient detail what he expects/orders.
