How many requeries/second can my server handle?
It answer is - It depends on many many many factors. How many cubes can you fit in a box is a similar question in a non technical sense. 

What are the queries, What are the specs of the server, is it dedicated mysql or does your webserver go on there too, Is it overclocked any ? Whats the temperature ? Do you cache querys ? 

The list goes on. The best answer is to just test it with your set up and a similar set of queries and see. We can not give a better answer