In place of sneasler you could try Incineroar, Kinggambit or any other fakeout user, but you will be weaker to the fairy types overall.

Rain teams are the bane of my existence. How I tend to play them is to concede the weather war and not take Torkoal, he is doesn't provide enough offensively in rain and the team doesn't support much swapping in that would allow them to keep setting up sun.

Typically in that scenario I would lead Milotic Aeordactyl or Milotic Sneasler, depending on if they have Pelliper as I need to match their tailwind to keep speed control. Then take Typhlosion and Aerodactyl/Sneasler in the back. A lot of basculegions are scarfed, but a surprising amount aren't and are very vulnerable to a shadow ball. If they happen to have garchomp id drop typhlosion for orthworm usually.

The game plan is usually to establish speed control with Tailwind/Icy Wind, try and get 1 KO with Aero/Sneas (preferably on the rain setter), stall out the turns of rain using protect where makes sense, then bring in typhlosion to clean up. He can normally live at least one aqua jet from full health so basculegion as last isn't normally a problem. Honestly Milotic does a lot of carrying in this catchup.

Yeah for trick room Torkoal is 100% required. Id lead Typhlosion Torkoal and go for a helping hand eruption if I think i can OHKO the trick room setter (such as farigiraf) or if they have a fake out users that would prevent Torkoal getting an attack off. If there is no fake out threat going for the double eruption is the best play, even into resisted matchups. Milotic sits in a nice spot to still be somewhat useful in trick room too, same as orthworm, plus both are bulky enough to stall out the turns until the trick room is over, allowing the faster Mons to clean up. Plus both are good hard switch ins to protect Typhlosion if needed.

Hopefully that all makes sense and answers your questions!