On our pre-kid days, on of our friends organized a "supper club". These were mostly graduate students. They let dh and I do our supper as a combined supper, but it had to be nicer than everyone else going solo. It lasted several months, then of course, some of the grad students graduated.
So, first night up David (the Korean guy) did Indian food. It was a couple of dishes that he made and then a few of the pre-made pouches. Family-style, with rice and naan.
We also had pasta made by the Norwegian, Chicken, rice and peppers from the girl from Washington. We made a roast beef, mashed potatoes, rolls, key-lime pie and a vegetable for our night. I can't remember what the guy from Finland made, and we went through half another round too. It was 15 years ago.
Around the same time we had friends that we played volleyball with on the weekends, and we alternated dinner at each other's houses.
After kids, we started hanging out with the neighbors, and we occasionally have a last minute (want to come over for dinner?) but more often than not, we are more likely to trade babysitting.
So in the last couple of years we've become friends with people in then neighborhood and they have a standing potluck at the park on Sundays at 5:30 pm. So that's really nice - it's family-style. Some days it's all takeout pizza, but that's rare. Most times it's a wide variety of salads, mains, sides, desserts, and wine. Now that it's dark early, we switched to brunch (first time this year).
As far as how many people goes -
Pre-kid days we also did big Thanksgiving dinners, from 10-14 people. Maybe more.
We also did dinner parties from 4 to 10 people.
It's important to be relaxed about it and don't try to do too much. Wine, a main, a salad or a side, maybe an appetizer.
Make sure you have enough seating.