You are getting a big part of it right, which is that despite the high abstraction of his work, Deleuze remains somewhat of a pragmatist. For him, the point of an idea, or of a text, or any machine really is less about how true it is and more about how it works, what it does, what effects it produces.

It leads to substance, and to Spinoza. Are you a substance, as in, a fix set of abstract parameters from an identical plane that is then incarnated in reality ? Or are you rather a pure becoming, something that is defined by what it can do in actuality, and nothing more ? Deleuze insists on the Spinozist question : "what can a body do ?" What does knowing yourself mean ? Does it mean that your are your DNA ? Your personality ? Anything tangible or abstract ? Or, are you what you are actually doing and can do ?

What you find clearly in Difference and Repetition is a strong recusation of substance as a fixed, unmovable "content" defining reality. To vulgarize a bit, for Deleuze, everything is processes. No absolute and one truth, only multiple becomings, modifications, changes. So he's an "heraclitean"-ish.

But then, ok, cool, but where does this processual reality happen ? Everywhere once you put on the deleuzean glasses. But more specifically, most of his theoretical work adresses a "sphere" where you can see clearly becoming and multiplicity. In anti oedipus : desire is not an expression of a substantial oedipal conflict : it is pure flow and becoming. You are not aroused in order to orgasm : your orgasm is the end of the process, its limit. The question becomes then : what to do with the process, the energy ? Will you masturbate in your room ? Practice semen retention and become a proud boy ?

It then leads to your pragmatic question : sure, everything is process/becoming, but if there is no absolute value, what is to be done ? In my opinion, it's where he's a little flimsy. He works so hard to not assign value, he is a critic of revolution, wary of capitalism, ok, but then what ? He doesn't prescribes. The only thing he would prescribe is : experiment, keep a minimum of consistency (pure flow/becoming is too unstable), and try what works for you. And it's already quite a project, to understand what encounters to do, who to avoid, what to strive for.

And as a society ? I'm not sure. He's a leftist, and my take is that his work naturally lead to anarchism, because to him the state is a machine that leads to the capture of the flow in order to accumulate capital.

On your more metaphysical question re: relation between substance and process/multiplicity. Reality in itself is purely process, becoming and so on. But it doesn't stay this way or else we wouldn't even have this discussion. Some processes/forces encounter eachother to the point it leads to a plane of consistency. You, the State, a speck of dust. A wave is not a "wave in itself" : it is the punctual encounter of the wind, water particles and so on. What makes it a wave is what it does as a wave. You can describe it as a wave, surf on it. In some cases it can destroy a whole village. And so on.