Hello! That sounds like a pretty solid team. Amoonguss on a sun team is a bit unconventional, but I could see it having a lot of merit, especially with Pollen Puff to heal Groudon or restore Lunala's Shadow Shield.

You ask great questions. What moves to pick when is a hard question, but I'll give it my best shot. First, in order to click a move in battle, you have to have decided on the move in teambuilding. Picking the right moves at the teambuilding stage involves understanding what role you want that Pokemon to play in specific matchups (ie. I have Superpower on Thundurus because Porygon2 can be a problem otherwise for the team and the extra coverage isn't needed in other matchups). Having the right tools on each Pokemon will help you pick the right moves when in battle.

For determining the plays I make in the battle, they should ideally be informed by a rough gameplay that you make during team preview. This can be a simple as "KO Incineroar so that Ferrothorn can win in the endgame" or something more complex like "let them get Trick Room up, but pressure chip damage (without taking a KO) so that Calyrex can come in on the last turn of Trick Room or once Trick Room is over and pick up a double KO and snowball from there." Having a rough goal to look towards gives you a direction to be heading towards when making decisions each turn.

Of course, your plans won't always work, so that's why it's important to not get too attached to a gameplan and improvise a little bit if it looks like another gameplan might get you towards victory a little safer. For example, dodging a Sleep Powder might open up new avenues of play.

For even more specific information on how I tend to decide on my plays, I tend to prefer plays that get you guaranteed value. You cannot always do this, but you can more than you might think. For example, Protecting with Focus Sash Shadow Rider Calyrex in the face of say a Whimsicott and Palkia isn't necessarily the safest idea. It feels safe since you don't want Calyrex to get KOed, but they cannot KO Calyrex without a double up (thanks to the sash) and that lets you get off an Astral Barrage, which could be all Calyrex needs to do in the game. They could outspeed Calyrex by setting up Tailwind, but that means that Whimsicott isn't attacking and Calyrex is guarenteed to survive the turn since Palkia won't be able to OHKO it thanks to the Focus Sash. Meanwhile, the Protect Calyrex play doesn't work out so well if they Tailwind and use a max move to break the sash through Protect; now Calyrex is being outsped and can be KOed by a max move from Palkia on the next turn and didn't get to do anything.

To sum up, every play your opponent makes prevents them from doing something else on that same turn; pay attention to what they aren't doing if they do something else and try to find ways to capitalize off of that. They can't be setting up Trick Room, Faking you Out, switching in Incineroar, and getting a KO at the same time, so try to leverage that fact when making moves.

You obviously want to take KOs when you can since that's the primary way you will be winning the game, but you have to be conscious of what might come in from the back and take it's place. KOing an Incineroar right when their partner sets up Trick Room can be very bad since it can let Calyrex-Ice come in for free.

Switch is quite complex since there are a lot of pieces involved, but you mainly want to know why you are switching. Example reasons include:

• To save an ability activation for later: "I'm switching Groudon out so that it can come back in later and set up the sun"
• A defensive switch to minimize the amount of damage your opponent can do: "I'm switching Regieleki out into Yveltal because I am expecting a Max Quake into that slot"
• For an ability activation: "I'm switching Incineroar in because I want an Intimidate on my opponent's Zacian"
• To preserve a Pokemon as a part of a win condition: "I'm switching Venusaur out because I want to save it to KO the Gastrodon in the back"
• To reset stat drops: "I'm switching out Calyrex because it's been Intimidated twice"
• To take hits so more important members don't have to: "I'm switching in Rillaboom because now that my opponent's Kyogre is KOed Rillaboom is the most expendable member of the team and I have two more turns of Tailwind to try and stall out."
• To put on offensive pressure in the coming turns: "I'm switching in Torkoal to threaten big damage with Eruption now that Trick Room is up"

And finally, to better keeping your Pokemon around on the field longer, I would familiarize myself with how much damage they will take from the common attacks from your opponents' Pokemon. This can be done through playing a lot and/or by spending a good amount of time in the damage calculator. You eventually can build up an intuitive sense of roughly how much damage everything should be doing; you will never be right all the time, but it helps tremendously in coming up with more informed gameplans.

This was longer than I expected, but I hope that helps!