Hey, it's great to see more people interested in mapmaking! The mapmaking community is pretty small sadly so that's why you haven't gotten any answers. Your question is pretty broad but I'll try and give you some general advice
I'd suggest either starting your world in Journey mode 1.4 with a complete character, or in a Tmodloader world with Hero's Mod and/or Cheat Sheet installed if you're okay with playing on 1.3.5 for a while. This way you can have infinite items, blocks, and a whole lot of quality-of-life features. Another recommendation is to download TEdit, which makes it easier to create large structures and environments and also allows you to place certain inaccessible objects like locked chests.
From there on there are lots of different ways you can create an adventure map, depending on what kind of map you want to create, and what you find fun.
Personally I like worldbuilding and storytelling. When I made my first map I started by making up a story premise which had you travel from one part of the world to the other. Then I filled up the space in between with different locations, challenges and side activities, and made up characters and lore on the way.
Here are a few tips:
Make sure to test your map a couple times before you release it to make sure everything works as it should.
Don't be afraid to make big changes if you find something doesn't really work out.
Have somebody else beta-test the map for you, to give criticism and find bugs.
Balancing - give the player appropriate gear for the challenges they will face, so it's not too difficult or too easy.
Don't make the player walk too far without anything to explore or to do.
Learn as much as you can about Terraria, all the different enemies, blocks, items and mechanics, and try to use them in clever ways!
A little worldbuilding goes a long way in making a map feel more alive and interesting to play. If the player is exploring some ruins, for example, let them discover the backstory behind them! Perhaps its creators left behind a note, or a nearby character has heard some rumors?
Look at other maps, both for story/setting inspiration and for cool tricks to use for your own map!