Selecting requirements is not a one time operation, and is best thought of as an iterative process
as shown in the diagram below.
You will need to consider the user requirements, the flexibility of the system, trends in hardware
and software (including standards) and the legal requirements. Using these to evaluate the
systems and select what you want. The systems will then need to be implemented (and this
includes modifying the software to your needs and almost certainly modifying some of your
processes as well). having implemented the system you will then over time want to optimise it in
various ways to meet your needs better. There should then be a review process and the cycle