I will be controlling all NPCs, wild pokémon encounters, etc. In some cases, I will determine "gameplay" elements, such as when a battle is over, who has won, if a pokémon is caught, if it evolves, etc. However, most of this should be able to grow logically from your own prose, as collaborative writers of a work of fiction. If it isn't clear in the beginning, just ask in this topic as time goes on, and things will begin to feel more natural.
I will likely be making short posts here and there to keep things going. For example, I might make a post as simple as "Wild Shroomish appears", which implies that it has appeared and can/should be caught. I might also make posts as long and detailed as a full turn or two of a battle with a gym leader.
Catching pokémon shouldn't be something that seems forced or awkward. Because of that, you'll likely be able to determine amongst yourselves who catches what, and when. Use the guide that is posted in the above links to know what pokémon show up and where. Don't abuse this freedom of catching, keep your teams believable and varied. If I have to interfere, I will. Additionally, non-regional pokémon, stray pokémon, trading, etc, I will occasionally throw at you, so you won't be as limited, and it would keep things rolling faster.
NPCs:
Professor Willow - Professor of the Alett Region, he lives in Shell Village. His area of specialty is in pokémon lore and history. Unlike Oak, Elm, Birch and Rowan, Willow is less of a biologist and more of a historian/archaeologist.
Cliff - First Gym Leader of Felice Town, he specializes in rock-type pokémon and rewards the granitebadge.
Mackenzie - Second Gym Leader of Quartz City, she specializes in grass-type pokémon and rewards the seedbadge.
Rufus - Third Gym Leader of Sterling City, he specializes in fighting-type pokémon and rewards the brickbadge.
Daphne - Fourth Gym Leader of Kneeton, she specializes in bug-type pokémon and rewards the colonybadge.
Roy - Fifth Gym Leader of Star Coast City, he specializes in normal-type pokémon and rewards the vanillabadge.
Alejandro - Sixth Gym Leader of Grove Ridge, he specializes in ghost-type pokémon and rewards the shadebadge.
Vegas - Seventh Gym Leader of Rastpeak, he specializes in steel-type pokémon and rewards the forgebadge.
Avery - Eight Gym Leader of Personnet, he specializes in flying-type pokémon and rewards the cloudbadge.
Volkner - Elite Four member specializing in the electric-type. He would later resign and move to become a gym leader in Sinnoh.
Archibald - Elite Four member specializing in the water-type. He would later move to Hoenn...
Maxwell - Elite Four member specializing in the fire-type. He would later move to Hoenn...
Jade - Elite Four member specializing in the dark-type.
Despain - League Champion, favors the poison-type.
-looks at Volkner and others- Does this mean that this takes place before the events of the official games?