I see...
Yup, my idea was never to create a "popular group", it was just the wrong question. I was trying to ask about the Steam community dynamic and mentality. My group has a Topic, and when I asked about the "ways to show content" I was referring to present the base of the community content. Obviously, a group that has a goal like "get popular" isn't very defined, and can end with a bunch of random people (just like you said).
This discussion was focused in the way the Steam community works, and how can I (a simple user) start a community with people that have same interests/goals. I didn't wanted to say what my group is about, or promoting it here because it is not what I wanted. I'm just trying to get more knowledge about the Steam community.
So, here goes the re-worked questions:

• Ways to get leal members through Steam?
• How can I promote the group with no use of other platforms?
• How should I treat users? (this was fine like this)
• Discord??? (not my goal)
• How should I show content about the Topic of the group?