Couple things:

• Curry paste. Use your preferred brand, but I like Mae Ploy or Aroy-D.

• Coconut milk. If you're in the U.S., the only brand I've been able to find that is 100% Coconut milk and not adulterated is Aroy-d in paper cartons, not in tins. They all have "100% coconut milk" in big letters on the front. I only use this; the other stuff lacks in flavor and mouth feel.

• Fish sauce. Use your preferred brand; I quite like Tiparos and Red Boat, but my experience is not that varied; I have used "Three Crabs" but didn't like it as much as Tiparos. I would consider fish sauce a necessary ingredient, along with lime leaves (I have used kaffir lime leaves and regular lime leaves off a neighbor's tree, and did not detect a significant difference in flavor).

Attempted answers to your questions:

The paste:

• You skim some of the coconut cream off the top of the milk and fry it with the coconut paste. You can also use some coconut oil (virgin/unprocessed is best) for this part. I've found the curry paste by itself has a lot of sugar in it, so it tends to burn pretty easily so be careful with it.

The meat/veg:

• After frying the paste/cream until fragrant, I just stir in the meat and vegetables. After the meat/veg have been tossed/stirred with the paste a bit, I just pour in the coconut milk.

Seasoning:

• Fish sauce adds salt and savoriness ("umami") to the dish. I typically add some fish sauce to the curry while it cooks, a little more to taste after everything's done cooking, and have some at the table for people to flavor their individual bowls as they like. You will not notice the fishiness unless you add it in your own bowl. I use all four aromatics/seasonings you mention except for palm sugar. I don't sweeten my curries at all.

Diluting :

• I typically don't dilute the broth; I like my curries thick and hearty, and I find that some liquids will cook out of your vegetables and meats to thin the curry out a little bit. If I'm short on coconut milk or have added too much meat/veg, and the curry is too dry, then I'll chuck in some water. This does dilute the flavors a bit, but not a big deal.

Toppings (bonus) :

• I like to top my curries (I vastly prefer green and massaman curry to red/yellow/panang) with some crushed fried peanuts, fresh chopped cilantro, fresh or pickled chopped chilies, and fish sauce.