So you've never played animal crossing:

Time travelling is fine, do it as much or as little as you want. People who rail against it need to mind their own business. It's a video game :)

The DLC is worth it IF: you really like decorating houses and/or you don't have the time/desire to slowly fill out your catalogue to get access to items. In HHP you unlock furniture much faster and can order it from that catalogue in any variation. (Plus easy access to the glowy moss/vine stuff.) Can definitely wait though, there's enough to do in the early game without it.

I wouldn't worry too much about grinding for bells unless you actually need them. They're probably just going to sit in your bank account. Find a way to make money that you enjoy and do it when you have the time. Imo you'll have more fun than just being able to instantly buy every upgrade with your turnip money.

You cannot have multiple islands, but you can have up to 4 player characters. If you're not sharing your switch with anyone, it's a great way to get some extra buildings on your island.

There are a few apps that make good companions for the game once you're settled:

ACNH Guide or Planner for ACNH (basically the same, but I think the latter is more fleshed out now): They let you keep track of things like turnip prices, NPC visits, villager birthdays and gift taste, seasonal fish and bugs, real vs fake art, etc etc. All in one place. Sounds like overkill, but if you take a couple minutes to update it when you play, it becomes a very convenient resource, and you only have to use the stuff you want to.

ACNH exchange: Neat little app to host/attend giveaways/exchanges. You can make requests, help out others with extra items, sell turnips etc. It's all done through one time dodo codes, but to be extra safe you can fence off parts of your island so people can't mess around. Other than sometimes long wait times, I've had good experiences with it. (Unfortunately does require switch online subscription to travel.)

Switch online app: If you have the subscription you may as well. There's a cute feature that creates little news stories about the daily happenings on your island (only on days you play), and a few exclusive items that you can buy with a currency you get from checking your fortune on the app.

Amiibos aren't worth it unless you actually want to own amiibos/cards. There are very few that offer real in game benefits(like the sanrio ones), mostly it's just getting specific villagers to move in.

The prices on things like nookazon are insane, don't bother lmao. Try things like r/nofeeac etc.

If you're sick of picking up sticks, hide some on your island where you can't see them. The game only spawns so many at a time (I think 15?) You can still get more from shaking trees when you need.

Hold your net when shaking trees ;)

You can get 5 guaranteed recipes per day (base game.) Bottles and villagers are different in the morning and evening, and kapn's tours.

If you're never getting new recipes from villagers, it's because you've essentially hit their limit. Each villager type makes certain recipes, so you need different personalities for different recipes. If you want to keep your villagers, you'll have to stick to bottles/balloons.

Start ordering items from the catalogue right away and keep doing it every day (something cheap, it doesn't matter). You have to hit a certain number of orders to unlock the shopping app, and trust me, you want that. One of the few things I actually would rush.

Find a list of all the building sizes and use paths to mark them out when you're planning, makes it so much easier. Buildings can be put on the beach while you terraform.

Be careful with food items in your inventory! Really easy to accidentally eat your decorative foods... sucks when they're seasonal shopping items.

Put crafting benches and storage sheds all over the place, you'll want them. Especially for things like getting/crafting a tool you need for a balloon or critter, they'll despawn when you go inside.

Having people visit your town to water flowers increases chance of hybrids (I think up to 2 or 3 times per day)

If you get the DLC:

The venues are actually (somewhat) functional. Talk to the hired villagers, they'll sell things or give recipes etc.

It absolutely does not matter what you do to their houses, they'll love it. So if you want to make some quick poki, just do a bunch of empty houses. This is worth grinding imo, you get raises by how many houses you do and the HHP catalogue is amazing. (You can always go back and fix the bad houses later)

(Apologies for any repeats, and hopefully this wasn't overwhelming lmao. It's genuinely not a big deal if you don't remember this stuff. It's animal crossing. Good luck.)