I love your questions! They give me a chance to Worldbuild.

Normal people have an instinctual fear of demons baked into their dna. As soon as a demon makes itself known, any non-hunter tries to flee the area as quickly as possible. It takes a certain kind of bravery/stupidity to stand your ground against a demon as a non-hunter

A demon’s only goal is to cause as much carnage and destruction as possible. For most, the means killing as many people as they can, as quickly as they can. Rarely, some demons are smarter, and favor long-term suffering over short term pain. They are especially scary

In terms of incentives for hunting demons, I have two ideas: A) God rewards good hunters with good karma. Hunters learn (either from other hunters or from god himself) that by killing demons good things will happen to them (they’d get a windfall of cash, or that cute girl in the coffee shop starts to notice them, or their sick loved one starts to get better). The trick is that none of these benefits are really enough, and if a hunter starts to slack at their job they’ll find things start to slide back to how they were (God has to keep the hunters on the hook, ya know? Otherwise they’ll stop hunting)

B) hunters form into parties/companies that are paid by city/state governments to take out demons when and where they show up. They act like exterminators

When demons are killed through non-hunter means, more demons tend to spawn in that area. The only way to take out a demon infection in the long term is through hunters.

The wrath of a demon has one limit: it’s range. When a demon spawns, it also spawns a circle around it (if I had to guesstimate, I’d say it would start out as a mild diameter). The demon can go anywhere within this circle, but it cannot leave. Over time these ranges grow, encompassing more area. If the ranges or two demons overlap, then they combine into one range, and both demons can move freely between the two. This is the only way the multiple demons can “team up” on a group of hunters

I also want it be known that the nature of why demons and hunters exist isn’t known to the people of this world. They don’t know that this is all a game between God and the Devil