Don't think in terms of an "arc". Never have an Overarching "story"
Because you don't know what your players are going to do.
You will save yourself lots of time and effort by never wasting time on either.
Now, having a solid
campaign hook is a G
ood thing:
This is Wisdom.
Redhammer speaks truth.
This.
You should never really be able to plan more than one or
sometimes two sessions ahead.
The players actions should be the number one thing that drives play. You should be riffing off of what they do endlessly.
This, all it really takes is listing your primary Bad guys at the beginning of the game, and adding no more than a one sentence motive why they are doing what they do.
Don't go deeper than that. And you only need to do this for a small handful of your named baddies.
You just need the starting direction, the barest sketch: The rest will sort itself out during play.
Also:
Steal.
Steal ideas from anywhere you can. You've already mentioned looking over the dragonheist adventure. This is good.
Don't worry about trying to be "original". Don't even try.
Steal shamelessly.
More wisdom:
Never have a single PC that can't be dropped like a hot potato if needs must.
The game world is bigger than the PC's. The bad guys don't care if Harald the half-orc is no longer part of that meddling group of adventurers.
The most important thing for any good campaign is that the PC's have real agency within the game world.
They should not be tied down to a single Arc, Plot, or 'Story' of any kind.
Here is a good example of player agency in action and how it can affect a campaign:
About the time my players literally said "To Heck w/ this, lets run away and be pirates!" in an AD&D2e campaign... & what became of them at sea.
deathtrap-games.blogspot.com
Now this is a example of the players shooting off in an entire other direction than the GM initially hope for, But he was able to handle it because he was not fixated on pushing his ideas of how things should be on his players.
As Ralif Redhammer stated above; players are generally pretty good about grabbing adventure hooks and running with them if they have already bought into the core concept of the campaign. And always be mindful to not over prep. You don't need to work things out as much as you think you do. It is an easy trap that most GM's including myself have fallen into.
You need to stay loose and flexible. Because you players will always do things that you've never thought of.
Most importantly: Have Fun.
It is important to have fun running the game. You should be just as entertained by the antics of the PC's as the players are by playing them.
When GMing becomes a chore that you dread - that way lies burnout...
P.S. - One way I have found to help with reducing anxiety while running a game: Get rid of all Clocks!
Put your cellphone away and have no clocks anywhere to be seen. You'll feel less like you're 'under the gun' so to speak to "fill" game time.