That's right! I completely forget about the Battle Frontiers. Yes! It can work for me to spilt into five stories.First question: may I ask why you feel the need to explore each region? I know you mentioned wanting to make it a "saga story," but it sounds like you already know of three regions fairly well. Would that be enough? It would work as a trilogy that way - and you could always have large age jumps in between each one. Hoenn to Sinnoh, for example, could be a few years. Also, Hoenn and Sinnoh both have Battle Frontiers. You could have stories that take place there? That alone could bring you up to five possible stories.
Giving my time to play time seem to be limit because I have other thing to do to focus on.However, if you really want to write other regions, I would suggest simply playing the games more. Maybe even when you're writing the other stories, since it sounds like you have a lot to start with and lots of time to play the games. Or, you could watch playthroughs of the games online so you could skip around a bit (such as jumping over Gym Battles and trainer battles and grinding, etc.) to just get the story.
At the very least, I am more familiar with Hoenn, Sinnoh and Kalos. I decide to go with that. Yes, I already have a plan to have a deveopment later in Sinnoh. I would expand between Sinnoh and Frontiers.But you're also saying you don't want to have whole volumes for each region, because you'll lose motivation - which I agree with. Honestly, I would suggest picking your favorite region and writing a story just in that region alone. You could split your novel into parts - for example, maybe the first part is Hoenn and the second part is Sinnoh, and maybe nothing interesting happens in the first five gyms in Sinnoh, so you cut ahead to the sixth, or just where something interesting happens.
As my OC's age, she would be 10 for the head start before she get older. I would say it more but I didn't want spoiler here. Curious thing~ And yes, there will be disaster but it like take a steady step before reach a critical hit later on. At first thought, I would put her family came from the place in Kanto or Johto when the disaster hit but I decide I want my OC who does not know any about Pokemon, include her family. So I would say they came from other world where Pokemon does not exist there.Still, with all that being said, it's hard to give more help without knowing more about what you want to actually do with this story, specifically. So far you have a girl (what age, by the way?) who's coming from a disaster on her planet (where? how did they come to the Pokémon world? WHY the Pokémon world?). Already this feels like it's pushing the limits on acceptable realism, so would it be possible to shift that storyline into a disaster in the Pokémon world? For example, we know that between the Red/Blue/Green//Firered/Leafgreen and Gold/Silver/Crystal//HeartGold/SoulSilver, the Volcano on Cinnabar Island erupts. Perhaps your family could come from there, and that could be the disaster you work with?
In any case; good luck with this story!
I will be writing notes and getting a head start for making a story. Thank you for point out my struggle. I like how you point it out. I want to keep your quote as reminder! Thank you so much!