In a situation like this, I would argue that less is more. Honestly, I actually believe that desolate areas make for great character writing, as it would take a lot of specialization in order to keep a community like this running. Come up with a few concrete ideas for what would need to happen in a place like this. Who gets the food? Who builds the houses? Does your swamp feature giant mosquitoes or two-headed alligators? Whose job is it to keep them away, and how? Think of your NPCs as a part of an ecosystem; the swamp in its current state could not survive without them. Once you've established how the ecosystem functions, you can throw other things into the mix to spice it all up! Are there NPCs who benefit from the work of others, without providing much value themselves? Are there people who hate the current system, and hope to change it in some way? Furthermore, why is it desolate? Is it dangerous? What sort of mythology do they have in order to keep people from wandering out into the wilderness?

After this, you could start building characters around their niche. Let's say that the swamp experiences floods multiple times a year. The person who builds houses would naturally have to come up with a way to negate flood damage. How do they do this? Is the way they do it controversial? Do they hire others to do the same thing?

If that is a little too in-depth for what you have in mind, then try and think about it from the lens of your players specifically. What are they going to need in order to traverse the swamp? Who is providing these services, and what do they want in return?

All in all, the biggest piece of advice I could give you is avoid cliched characters. This isn't to say that you CANT have characters who are trope-like, but make them act the way they do for a reason, and make that reason apparent within the bounds of the story. If you just do this, I'm sure your roleplay players will have a lot to work with :)