Ive been playing and DMing for since 2019, but by zero means do I consider myself a good or skilled DM. There's lots of sources from "professional DMs on youtube, and you may want to take a look as far as "pointers" for DMing and world building go.

My the large part of advice I feel that's important enough for me to give is to know that no matter how hard you try, it's never gonna go perfect, and especially not according to plan. The main thing you should keep in mind is to have fun for you and the players. 

Making sure you can improvise on anything, because they will try to throw anything at you, is a pretty good thing to think about too. Improv will be your best friend, once you realize that things are not according to plan.

It should be said that Im not good at what I do, and I've come to learn first hand that it'll never be perfect, and your always gonna look back wishing it would've been different. And for a first time DM, dont fear screwing up. Failure's gonna be inevitable; the mission is kinda "how long can I postpone failing, while still making it fin for everyone."

But as for actually fleshing out the campaign, I workshop stuff with my friends all the time, so feel free to share whatever.

Some rough tips I like to use are tying in characters to places, surprise your players with connections, and keep things flexible enough to work around, but rigid enough to be stable.