Yes you are right. I suspect that only males would use this slang.

It's equivalent to "What the hell is going on here?" However, it's very immature sounding. The only people you would probably hear this coming from are teenagers.

Kind of, although I would say the phrase "what the balls is going on here" is a lot more juvenile. I most heard that phrase when I was in high school, and from teenagers. In a professional setting, you might hear someone use the phrase "what the hell is going on here" but you would almost never hear "what the balls is going on here". That would probably get you a few funny looks. Hope that helps.

I have never heard this expression before but my guess would be yes it's the equivalent to 'what the hell is going on here ?' With balls in this context referring to 'testicles' (i.e. male genitalia).