I'm afraid that the actual set of tools is classified for now, sorry. You can see it as soon as you're accepted as a mod~
You can if you want to, though it's not immediately necessary since just picking things that seem balanced works well enough (and mods are allowed to give the occasional trainer that's not "random" anyway). Honestly the only guidelines are to keep things roughly equi-evo and equi-level, try to avoid teams that are too long or too short (1 or 5-6) without appropriate balance, keep the pokémon in-region and try to avoid unown, fossils, pseudolegends, starters, the dinobots, makima and the pokémon that evolve via Logos stone or in the ruins (but not their prevos; cherubi/cherrim are okay, cerisol is generally not). Beyond that teams can really be whatever. *shrug*
OI's trainers are generally easy (barring the ever-present RNG hate that makes it not seem that way), yeah, though I think that's largely due to the use of straight-up game mechanics in a play-by-post format. Not sure if I'd consider AI trainers from the games the same difficulty or easier, but either way you can get through even tough ones with just a few button presses as opposed to waiting days to beat a single guy. Making the trainers relatively easy compensates for that a little. There are also the requirements, and I think maybe that gives people the mentality that they need to be able to get through trainers quickly so as to keep moving toward that goal. Turquoise generally doesn't use requirements like that, at least, so if someone did feel like having a longer, more strategic battle then they have that option and don't necessarily feel like they have to rush. The battle mechanics are largely identical, though (kinda wish we were doing something else but ehhh gonna have to try and work that out later), so since they'll be equally not fun to spend days and days and days on the difficulty should keep that in mind. IDK, maybe we will want to tweak how easy or difficult trainers are down the line, though we'll also need to mess with the experience payout if that's the case.
(I think what OI does is assign each star rarity to a percentage, like maybe 0 stars is 50% and 5 is 1% with whatever else in between. The mod rolls for a rarity and then rolls an even chance for any pokémon within that star bracket. Which, of course, presents the aforementioned hiccup when the list of pokémon for any given star rating gets longish.
Some of the star images work, some of them don't; depends on which forum you're looking at. Quite a few are using an old source URL and haven't been updated yet.)
@edit: uhhh... no? Not sure what you're talking about.