Well, come on!

Memory, processor or disk is not everything

When it comes to infrastructure, having a strong processor, a disk drive with high I / O, or even 64GB of memory may not support large requests per second. You need to analyze everything for scale.

Database

MySQL may not be the most recommended for you, you can opt for NoSQL banks, which will improve your performance much more. It's also interesting to study cluster that divides loads, work with various nodes .

Study implementation for example of Redis , Elasticsearch , MongoDB , and so on. Each engine has a proposal that works best with specific issues, study your case.

PHP

I'm developing PHP, but I put in check-mate with one question: is PHP the best language for this purpose of large requisitions? Have you studied other approaches? What's the point? What expected result?

Scale and not-shared

First, you need to understand what load balancer and how it can help you with scale servers that you will need to provision.

Your infrastructure should be all interdependent and have fault planning.

To finish

Your question is too generic, since to ask if x or y can handle x or y requests per second on x or y conditions is too big, it is not so simple infrastructure. Nowadays there are several technologies that can abstract greater responsibility with lower costs, for example Docker . If you have in your hands the development of a system that will receive this load, the interesting thing is you look for people responsible for their respective areas such as: Database, Infrastructure and project manager. Many details will be taken into account, so only you can build a scalable infrastructure, cheap and above all strong:)