300 inserts per minute, 6 million rows per month
There are basically two ways to answer your question: speculation and simulation.

For the former you still have not provided much useful information, such as:


What is your current workload and how does your server behave today?
What are your current data volumes?
What are you planning to do with your 6 million new rows a month? Keep them indefinitely? Archive them after 3 months?


As for simulation, it would likely take you only a day or two to clone your existing database, creating a test system; download and install Apache JMeter; write a simple test plan generating your 300 inserts/second plus your queries; and run it to see how the system actually behaves under your projected workload. This will let you (or a temporary consultant, as suggested by others) to identify performance bottlenecks and determine whether they can be resolved by throwing additional hardware at them.