1. It's pretty common for people to live in New Jersey and commute to Philadelphia for work. It's a little less common, but still frequently done, for people to live in Philadelphia and commute to NJ for work. A 20-minute drive isn't terribly long for people who are already used to commuting, but your church would have to be exceptional. If your church is a lot like the church that's two blocks away from where someone lives, they're likely to prefer the church that's closer. Note: Some South Jersey locations are near commuter rail train stops. Commuting from Philly is easier if your location is near a train stop.
2. Philadelphia exerts a strong influence over South Jersey. They provide our TV and radio stations and our newspaper. Philly is often where you go if you want to see a concert, museum, or sporting event. Philly is very congested, and then the congestion eases up the farther you get from the city, so that by the time you're out in, say, Salem County, it's pretty rural. Churches with strong families and a mission emphasis are pretty common in both Philly and South Jersey, so you'd fit right in.
3. Cherry Hill isn't really a small town; it's pretty congested and sprawling. Lots of businesses, lots of traffic. A high percentage of Cherry Hill's population is professionals -- doctors, lawyers, etc. I've only been to Haddonfield a couple of times, but it feels more like a town, if I remember correctly. I'm from further south, in Gloucester County, and we do have genuine small towns in my area.
One additional thought: The northeastern US has a reputation for being non-religious, and it's true that we have a lot of non-religious people here. But we also have lots of churches here: Catholic, Orthodox, most of the mainline Protestant denominations, multiple conservative or Fundamentalist Protestant denominations, multiple Pentecostal denominations, and nondenominational Protestant churches, as well as SDA, LDS, JW, and Unitarian. You're more than welcome to come and add your church to the list of churches in the area, but be aware that you wouldn't be coming into a nonreligious area to present the gospel for the first time to people who've never encountered Christianity.
We do have a fair number of lapsed Catholics and similarly lapsed Protestants in the area -- people who grew up in church-attending families and maybe were baptized, but who have no interest in the Christian faith. If you could reach them -- if you could present the gospel in a way that they could truly hear it and see how it could be relevant to their lives -- that would be a good ministry to have in this area.