Alrighty, let's see.
Background: I've been at Georgia Tech for longer than I'm willing to admit. Bachelors, then Masters, then PhD, then adjunct instructor. All in computing. There's a very real possibility that if you come here, I'll be your instructor at some point. Hi.
My first two years at Georgia Tech, I hated it here. Classes are hard as fuck. I got a 28 on my first test here at Tech (Calculus II with Bellissard). I cried. It was rough. Toward the end of my Bachelors, though, I started to regard Tech differently. Tech was a worthy foe that I had managed to conquer. I looked at the other people in my classes as intelligent because I knew they wouldn't still be here if they wouldn't. There's a sense of camaraderie that comes with knowing we all survived the worst the school could throw at us. It's almost like a fraternity, except instead of paying for your friends, you're paying for a diploma that really has meaning in the world.
Starting closer to the end of my Bachelors, and continuing through my Masters and PhD, I started to realize something. The early classes are hard as fuck for a reason. That reason is that a Georgia Tech diploma actually means something. It might be true that you never really use the things you learn in freshman Calculus and Physics, but the fact that you can pass those classes says an enormous amount about your ability to learn, work, and apply yourself. When I hear that someone got a Bachelors at Tech, I immediately respect them because I know the kind of work it takes to get that accomplishment.
College is the only time in your entire life when you have the leeway to devote all your time to bettering yourself. Some people take that time and treat it as a four-year vacation before they have to enter the real world. Others treat it as the investment it is. At Tech, you're treating it as the investment that it is. I worked my ass off during my undergrad. I can't remember doing anything except schoolwork. I worked pretty hard on my Masters. PhD is a different animal. But now, on the other side of it, I honestly have what many would consider a pretty cushy life. I make six figures at 27 years old. I'm married with a kid, my (gorgeous) wife is a stay-at-home mom, and I have incredible income to spare. I'm working on a couple startups, building my own house, and I'm an investor in several businesses.
So, make no mistake: if you come to Tech, you're going to work your ass off. You're going to hate your life for a couple years. You're going to doubt your decision. And then, on the other end, you're going to set yourself up for a great life, making plenty of money and having lots of options regarding what to do with your career. Or you can take a four-year vacation from the real world, and then spend the rest of your life catching up with people like me that treated college as the investment that it is.
Now, regarding your specific questions:
The invention lab and maker club are open to all students.
The Mini 500 is mostly for fraternities, I think. Don't join a fraternity, it's a waste of time, money, and your liver. There's plenty of other events to participate in.
I took a pretty wide assortment of classes throughout my GT career. Lots of psych classes, a few economics classes, a couple engineering classes. One of my roommates took astrophysics, but he was a physics major. Still, as a CS major, you'll have plenty of free electives you can spend on what you want.
The "teachers" aren't here to teach. They're here to research. That's what brings Tech money, and that's what gives Tech the reputation it has. As an undergrad, I hated this. As a graduate student, I loved it. When you take a class at Tech, you're not taking a class from the best teacher in the world. Instead, you're taking a class from the person who is actually building their own field. You're taking classes from modern Einsteins, von Neumanns, Hawkings. They're not the greatest teachers in the world, but they're incredible minds.
Overall, after spending my entire adult life here, I wouldn't dream of being anywhere else.