The Many-worlds interpretation of QM does not mean that different universes have different fundamental constants. If that were the case, the fundamental constants could change in value each time a quantum measurement took place.
The universe might be infinite in extent (e.g. Einstein-de Sitter) even though at any time you can only see a finite part of it, so even though the probability of life in any galaxy might be vanishingly small, as long as it's finite you can expect life to emerge somewhere.
Supposing our universe is a simulation, possibly running inside another simulation, etc. At some level there still must be a ground reality in which the first simulation was made. So, there needs to be at least one level, which appeared out of nowhere, or always existed, in which computers can be built to run the simulation.
I'd rather not have to repeat the same points I made in an argument I had here previously, as no one seems to change their mind about these things, but I can't see any way that NPCs in a virtual reality/simulated universe can be conscious - even though they might appear to be - so I think that if we're in a simulation, consciousness must be based in the universe which is not a simulation.
It might be possible for the fundamental constants (and, indeed, the laws of physics) to be fine-tuned, but only in a simulation, by its programmers.
The idea of a creator God (of any non-simulated universe) has no explanatory power. All it does is hide complexity inside something supernatural. How would this god appear out of nothing?