Ooh, nice. It's cool that Pokemon Essentials gives you the scaffolding for something like this, even if the provided sets are... questionable. One question that I thought of while reading this:
You definitely plan to have rewards, and I remember an earlier post of yours mentioned that you planned on having them be nice. To that, do you plan on having some of the rewards be one-off for the first time then something more generic and repeatable (like Candies) after? For example, there's still a glaring amount of TMs that simply aren't in the game (Ice Beam pls), and I imagine you'd want them all to be available in some way eventually. Of course, if they're just all going to be found in the copious amount of Legendary quests that could also work. There might also be some other cool items to put there, but I'm not creative today.