Wanna talk about Adventures some, since I definitely had some reservations. I only did the tutorial one, but the datamine thread had a few others that seem in-line.
I also haven't done this online.
First off, the rental Pokemon seem fairly competent. More than you'd expect. I had no real isseus with my rentals as I progressed through the den.
With the CPU you get right of first refusal. It generates 3 pokemon, you pick one, then it's replaced and the next down the line picks one. Not sure if CPUs just pick at random or what. Repeat until everyone has one.
You have 15 seconds to pick a given path. CPUs just auto-agree with you. You can take a second to view teh entire path if you like, too, there's no hiding what's where beyond hte smoke clouds.
The paths will sometimes have NPCs or berry patches. Scientists will let you swap out a rental Pokemon with a new one if you like. Adventurers carry 4 items, you get to pick one if you like. Mine had an Eviolite (useless for us), Blunder Policy, Muscle Band and a Misty Seed; I assume these are randomly generated. I actually didn't take a good look if the CPUs took the remaining, but I think they did.
So, the Pokemon themselves seem like they can be anything in the game? I ran into an alolan dugtrio and a g-max alcremie. Again these movesets aren't half bad. They seem significantly easier than normal. None of them ever put up barriers or anything; I also didn't see anyone use a g-max move but that always seems like RNG. They go by at a pretty fair clip, which is good.
When you beat a pokemon you choose to catch it (this DOES take a ball, by the way). If you catch it you, again, get right of first refusal. If you pass on a Pokemon after catching it, the CPU get to decide and by that I mean the first CPU took 2 of the 3 pokemon i left behind instantly, lol. Oddly, for the final selection, no one took anything. Maybe they thought they had a good match-up as-is for the final pokemon? NEeds more testing.
For my tutorial I got Suicune. Not sure if that's the same for everyone's first time. This was...not very hard! Again I didn't see any barriers or max moves. Suicune did get anxious as its helath got below half and started doing 2 moves a round, though. I suspect that the "stronger" legends will probably put up barriers and such, though.
Once the adventure is complete you can choose one of the Pokemon you caught. this includes the legendary. So I had an Alcremie, a Dugtrio, a Metang and Suicune to choose from. This selection stays even if someone else rents the pokemon or if you passed on renting someone. But I had to pick Suicune if I wanted it, the others are just released.. You Do get to check its stats and movepool so I suspect that if you dont like it, you can set it free and find it again later?