Question: Does the fact that space is expanding actually mean that the no. of particles that get created and destroyed from nothing is increasing or what is the space that we say is expanding made up of?
Yes, you’re right. The number of particles created and destroyed from nothing is the same across all empty space (the so called “quantum vacuum”). So as space expands, so does the number of particles being created.
It’s not constant around other particles though: it increases. We say that some types of particle are able to “polarise” the vacuum. Complex particles like protons are really more like a water-droplet of short-lived particles, forming a “cloud” around the three quarks around the proton. And just like a water droplet, these short-lived particles are held together by a tension. This makes the proton’s structure extraordinarily difficult to understand.