Questions already asked and answered

We've been introduced to two different Main Characters, on two different continents so they are extremely unlikely to meet anytime soon, but since the World was split are they on the same 'Earth' and tied to that is there going to be more about the various worlds or was that a one-time thing to cull the population and infrastructure?

The splitting of the worlds is mostly a one time thing to shake things up, keeping as many humans alive as possible while removing the existing social structures and infrastructure. Both Jen and Rob are on the same Earth, and most of the story will be centered on that specific world.

Do you listen to any music when you write, and do you have a playlist for Jen?

I like to have music going in the background, but very rarely is it something to set the mood, more just something to fill the air. I'm willing to give most songs a try, but as of today my 3 most played artists would be Imagine Dragons, Ludivico Einaudi, and Chris Thile. Jen doesn't have a playlist, but her theme song would be "Sound of Silence", by Simon and Garfunkel.

Is Jen going to be considered powerful when she breaks out of the cave? I can't imagine many other people survived as difficult circumstances as her, but her resulting skillset seems less overtly powerful than Rob's. I wonder if the forces that trapped her there did it to hamper her growth (compared to surface dwellers).

Her power level is above average. She's gone through some intense struggles and her paths and skills reflect that. The main thing holding her back is that she doesn't have anyone else to interact with, to get ideas for self created skills from and to share information about the system with. On top of that, she's going for a caster style build, which is much slower to pay off than a more physical skillset. Physical skills and improvements are easier to process and integrate than magical ones, iven their relation to pre-existing abilities, while spells and mana related abiltiies have to be learned from scratch.

how many 'energies' are there to account for in the metaphysics? Just mana, aspected in various ways? - or mana, qi, karma, faith, psychic energy, soul motes, chaos shards, System bits, etc, all interacting with each-other?

Everyone has three pools that the system tracks.

HP, otherwise known as life-force, life energy, hearts, and more; tied to the body's physical condition.

Stamina/energy/Skill points; motive energy used for physical agumentation and motive force.

mana, qi, karma, faith, psychic energy, soul motes, chaos shards, System bits, etc; Esoteric effects.

The system is responsive to whoever is using it, appearing in whatever language they are most comfortable with, and using terminology that they are familiar with. It's the same energy for everyone, but someone who thinks of it as qi is far more likely to develop a cultivation Skill, not because it's only possible for them, but because it fits their mindset better than someone who would think of it as faith.

Maybe she can learn alchemy and keep going the magic/nature route she seems to be going. Will she befriend the wildlife or struggle for her life?

What Jen does or does not do will have to wait for the story to get there, but on a more general level the wildlife is mostly unchanged. The reversion to a more natural earth did reintroduce some species to areas they didn't previously inhabit, but this isn't 'The Birds', where every sparrow is suddenly a murderous level 0 out for blood.