Excellent questions! I'll try to answer the ones I have ideas about.
Group classes are a great way to improve your dancing, especially since you're still at the beginning stages of learning how to dance. I was very shy about starting group classes, too, and it was over seven months before I was willing to do it. It was a shock for me but it was excellent training because it really made me start to understand how I had to dance so as to be able to dance with any of the leaders in the class or any people I would encounter social dancing -- not just dancing with my teacher and being used to only one person.
Classes may work differently in different studios, so it's a good idea to go watch one to see what you think. I'll answer your questions about how classes work based on my own experiences.
The studio I take lessons at "balances" the classes so that there are never more than two extra leaders or two extra followers. The teachers have everyone rotate partners about every 5 or 10 minutes, so no one is left alone for very long and no one is left with the same person for very long.
Ballroom doesn't really need never-ending gimmicks to sell lessons, because dance itself is a never ending quest for personal development, improvement, and and achievement. That said, some studios do use such sales tactics. However, not knowing how your studio works, I can't say anything about what is really going on there. It could be that they've divided the bronze syllabus into four parts to make it easier to learn (biting off smaller chunks, as it were).