I'm not sure if you're still looking for responses to this but I have some experience with this. I'm relatively new to the scene and other people might have had very different experiences so just treat this as one datapoint.
1. The Internet makes it pretty easy these days. There are a few major swinger websites that are kind of like online dating sites and have local events listed. A couple new to the scene can join one of those sites and meet another couple to get to know privately or go to a public event. Once you have friends in "the lifestyle" it is easier to meet more people and hear about more events and groups. Obviously there are other ways to get into it but those sites make it easy.
2. It depends on the group. There are a lot of events that are completely open, as long as you are a couple and follow the rules (mostly around getting consent before doing anything that could be in inappropriate) you are treated like any other attendee. At those events there is usually a main social area where you meet with other couples and find people you would like to play with, and then head off with them to a play area if there is a connection. For example a lot of swinger groups do "hotel takeovers" where you rent a room and if you meet people you want to play with you can play in the hotel room. Other groups are more private or exclusive, where you have to be invited in or just have to be friends with everyone. In groups where everyone is friends there can be more of a free for all vibe although things like consent are still very important.
3. It tends to be a common issue for new couples that are just trying things out more than anything else. Sometimes the idea to open things up is mainly being pushed by one half of the couple or swinging is trying to be used to save a relationship that already has serious problems. Both of those situations will generally lead to big problems such as someone leaving a play session in tears or a couple getting into a heated argument. Also a generally tricky aspect of swinging is that it's not trivial to find two couples that are fully compatible across all four people, sometimes one half of the couple might feel like they are "taking one for the team" too often by having to play with the partner of someone their own partner is into even if they aren't attracted to that person. Couples that have been in the lifestyle for a while tend to have worked through a lot of those issues though and are usually very good at communicating and making things work.
4. Yes I would say the overall lifestyle can be somewhat clique-y where there are established groups of friends that have known each other for years. These smaller groups might also invite each other to private parties. As a new couple it can be easy to find people who want to play at open events but harder to be accepted in some of these smaller groups. This probably depends a lot on where you live though.
5. I would say it's more like dating. Not everyone is treated equally in terms of being able to get a date but there's no heierarchical structure. A fit young for will tend to get a lot more interest than an older couple. But even with those issues it's not that hard to find people to play with. The one explicit "lower class" in the lifestyle is single guys. Generally if an event has a fee associated they have to pay more and some public events bar them entirely. A big reason why this focus is on single men rather than single women is that a lot of couples look for a female for MFF threesomes but it can be difficult to find one (in the lifestyle single women looking to play with a couple are called "unicorns")
6. Everyone is different and has different limits. I would say that the swinger community is much more open about sex in general than most people so sharing explicit details tends to happen more than in vanilla settings. Some people are comfortable playing in public areas where anyone can watch and others don't even want to play in the same room as their partner when they pair off with a couple. It really depends on the specific people involved.
One more thing I should mention is that at least where I'm from there is also a big polyamory scene that has some overlap with swinging but is also a distinct thing. And there is more of a very active BDSM focused community centered around FetLife that has a lot of events and meetups. Once you start meeting people in any of those three you will tend to run into people who are friends with or play with them but more fit in with those other groups.