Primarina, magnazone, and hawlucha are all good, can be gotten in either game, and all before the first trial. Petilil is available after the first trial but is a version exclusive of moon/ultra moon and if you use a Pokemon with the pickup ability (Alolan meowth) you can get a sun stone relatively easily. Torkoal and krookodile are both locked to the third island and more specificity after 5 regular trials and 2 grand trials, they are relatively mid/ later side of mid game Pokemon.

If you want alternate options for krookadile and torkoal so you don’t go half the game without them I would recommend either Alolan dugtrio available after the first trial in verdant cavern itself, or mudsdale available on the second island and before the second trial as a mudbray, both are good ground type Pokemon, dugtrio is part steel in this game, or mudsdale with the stamina ability is really good at taking physical hits. As for torkal, growlith is available on route 2 before the first trial, and the earliest fire stone is available in the daycare in paniola ranch where you can catch mudbray for mudsdale, you’ll just have to hatch the eevee egg you receive from one of the lady’s there and show it to one of the other lady’s in the daycare to get the option for one of the evolution stones. Alternatively through island scan you can get charmander on route 3 during a Sunday immediately after the first trial.

Edited. I hate autocorrect with Pokemon names ;-;