The cardinality of a many-worlds multiverse isn't clear. It might be finite if all physical systems are in a superposition of a finite number of eigenstates in the collapse/split basis. You're also not creating anything out of nothing. The correct version of your complaint is "Let's create x > n things out of n things" (where "things" are quantum states), which happens all the time when you take the tensor product of two quantum systems, evolve the new overall system, and end up with a state that's not factorizable into a tensor product of two states.
Keep in mind that the infinite universes still obey conservation laws collectively.
I tend to think of it like the number line. There are infinite numbers between 0 and 1. If we decide to define infinite unique ranges between 0 and 1, the space each one occupies becomes infinitely small and the total range is conserved.
But we don't know whether the multiverse is infinite or not, so that corresponds to the question of whether the range is from 0 to 1, or 0 to infinity.
Either way, the original point stands, and unitarity of the wavefunction (the most notable conservation law) is maintained in Many-worlds.
Where people get confused seems to be a mix-and-match of incompatible parts of the Copenhagen and Many-worlds interpretations, where you have both universe-splitting and the non-unitary wave function collapse in the same flawed interpretation.
Pilot wave theory still requires the wavefunction to exist, with all the same detail as many-worlds, all the same computations. It just then picks a particular timeline and declares that this one is real, these are real particles, and everything else is shadows on the wall. It's thus incompatible with computationalism.
My limited understanding is that the pilot wave is more of a concept regarding embodied in the exact state of the universe. In other words, the pilot wave is the seed in the pseudorandom number generator of the universe.
I'll admit it does get a little philosophical, but:
No. The "pilot wave", in pilot wave theory, is a mathematical object identical to the universal wavefunction of the many-worlds interpretation. As such, if you believe that computation is all is required for consciousness to exist (and there's no separate "is real" tag on the math), then it's an incoherent concept.
I fall on that side myself, but I can't convincingly argue that it's the right philosophical stance to take. I've yet to see anyone give a proof, it just seems most likely.
No, non-determinism on its own can't reproduce all the predictions of quantum mechanics. That'd be a different theory, and one I believe has been disproven experimentally.
Mathematical solutions are never guaranteed to be physical, or even potentially realisable.