They're gonna fire the World Cannon

Steve,

Your questions are all good questions. I wish I could answer them for you, but it has been more than twenty years since I studied Elementary Particles and Relativistic Quantum Field Theory. I've forgotten a lot and what I remember is probably out of date.

In the Standard Model there are a dozen fundamental fermion particles plus a dozen corresponding anti-particles. These are things like quarks, muons, electrons, neutrinos and taus. There are also a few a few fundamental boson particles.

Certain combinations of these elementary elementary particles make up all of the other non-elementary particles (like protons and neutrons). The boson are typically the particles that mediate the forces between the other particles. The photon and gluon are probably the most familiar.

I'm not aware of any framework that forbids gravity from being included into the theory. One of the problems is that we just don't know how to do it. A graviton particle has been postulated, and experiments have been performed to look for gravitons. Other theories, like String Theory seek to include gravity in other ways.

It is also quite possible that there is yet another, fith force, lurking out there. Some of the puzzles related to Dark Matter suggest that there may be something else. So all of your questions are good, and people are working feverishly on each of them. We just don't know the answers yet.

Apologies if some of my information here is wrong or out of date. Like I said, it's been a long time.

As a philosopher, you must know that the first physicists were philosophers.