Hey Kurnikr,
Hard to tell at the moment how long the story will be because is not completely written yet. I have a basic idea on paper on how the story should evolve, but I write down the story little by little. That way, I keep the story flexible when I come up with new ideas. I don't know what is your definition of 1 or 10 miles long, but I'm aiming for at least 1 hour read time for each girl, roughly 5 - 6 hours if we count all of them. One sure thing, I will not do a never-ending story like Giant Guardians game. (I do love the Giant Guardians game, don't get me wrong, but they introduced too much characters so they stretch the main story for nothing IMHO.)
Hard to tell how many version I will do at the moment, but I would say if at version 0.7 the story is completed, it's possible I would jump straight to version 1.0 and mark the game as final. Each micro version will be dedicated to expand the story for a specific character or two and when I switch to a major version, 0.2 or 0.3, there will be a special event that will involve all the characters. (For example, a trip to the beach with all girls, or when the MC will go back to his own world and one of the girls will follow him.).
Once again, it's hard to put a number % wise for each character update, but I would say 10 - 15% maybe. That's doesn't sound like a lot, but if I manage to expand two characters story in a single update, the story will progress fairly fast. I aiming to finish the game within 2 years at max. I do not plan for any continuation because I would like to start another project after this one. If peoples would like a season 2 for this game, I may consider it.
Lastly, Riley will be the farmer girl and she will be introduce in 0.05 release.