This is a little bit of a tricky question because it is homework and a direct answer would simply equate to doing that homework which is not what this website is about. Apart, from the purely technical bit of the right decisions, which you should do entirely on your own, I am interpreting this question as "There are so many options out there! Where do I start? I am lost!" and I am providing the following answer on a general framework that can be used in these cases.
Very briefly: Use a requirements matrix to rank your options.
The requirements matrix lists each of the requirements of the project. These are already available (Minimum sampling frequency, C compiler, number and type of I/O, real-time requirements, etc). Some of the requirements of course will need further unpicking. For example, the requirement "Capable of doing sound localisation" immediately leads to the question of "How accurate does this have to be?" which tightens the requirements of sampling frequency and data processing. Is floating point processing required or fixed point? Is the board fast enough to emulate floating point? And other similar considerations.
For each design option, add one column and provide a simple answer of how well does it cover that requirement. For example, suppose that you have an audio design project and your possible implementation options are Product 1, product 2, product 3, ... and each one has different ways of providing an audio output (Simple filtered Pulse Width Modulation, audio chipset, virtual sound card, etc).
At the very minimum, this matrix will help in selecting the one option that covers the most requirements for the design. More elaborate scoring scales are possible but also application dependant.
For more information, please see this link.
Hope this helps.