Tips for creating a 5e 9 hells campaign

So, I’ve never dmed before, but I had an idea for a 5e campaign where the party fights the final boss immediately and they tpk them and the entire actual campaign is the party fighting their way through the 9 hells to make their way back so they can kill the final boss in a rematch.

I love the premise, but I don’t know the first thing about actually writing a campaign. If anyone has any tips or maybe some tools I could use, I’d really appreciate it. Feel free to also give constructive criticism on what I have already.

What I’ve got so far is that they meet up in a village at lv 5, a vampire comes in and announces that she’s going to enslave the village to act as an infinite food source, then if they attack she kills them and if they don’t then she says she’s actually hungry right now and she attacks and then she kills them. They wake up to an unbearable heat, the smell of sulphur, and distant screams of agony. They must fight through the nine layers, the lord of each layer being the last fight of their respective layer, and after each layer they level up.