>>9787315What scale? If it's pretty small, you could buy plastic figures and modify/paint them; apoxie is a good material for making modifications and pretty easy to work with. At very small scales like railroad there are probably some firefighter sets you can buy. If you're thinking something bigger like 1/12, you can buy unclothed dolls at that scale and make them firefighter outfits.
If you have money to spend you can use something like hero forge, it can give you some okay naturalistic figures if you adjust the posing a lot, if you don't mind the chunky proportions.
I think you need to figure out what scale you are using, based on what size you want the diorama to be and what size you are comfortable working with. 1/12 outdoor scenes would quickly get unwieldy. It sounds like you might like a train scale, and if you pick a scale to stick to it means there will be more options for things to buy premade for your diorama rather than building every part from scratch. Train scales also have a lot more outdoors type items compared to dollhouse scales.
Here's a quick rundown on train set scales:
https://www.trainsetsonly.com/choose-a-scale.htmlHope it helps
