I'm going to avoid discussing the details of my own experience, as it's very personal and I'm wary of how much I share about myself on a public forum. If you contact me by PM we may be able to set something up.
1) In regards to your legs, you're basically fucked. Goenka places a strong emphasis on equanimity (upekkha), which is key to his understanding of increasing human happiness. In his model, much of human suffering is caused by what he calls sankharas, which are essentially bad psychological habits of craving for and aversion to external stimuli.
The idea is that when we experience something pleasant, we generate lots of craving and clinging. Then, when that pleasant thing inevitably disappears, we are disappointed and suffer unnecessarily. The pain of a breakup, for example, is largely caused by our own clinging to good things of the past.
Likewise, when we experience something unpleasant, we generate anger, hatred, and ill-will which cloud our judgement and make us suffer more. We can stay pissed off at a coworker for days because of one negative comment.
In the Goenka tradition, body sensations are used as the main meditation object, and throughout the retreat one will come to observe both pleasant, tingly, fuzzy sensations, as well as the unpleasant sensations of aches and pains. In his model, applying equanimity to both sorts of sensations undoes the sankharic programming, and leaves you capable of responding to events in daily life with more centeredness, peace, and clarity.
So yeah, your legs will fucking hurt like hell, and Goenka is of the opinion that you can work with that pain skillfully in order to make yourself a happier person for the rest of your life.
I do not necessarily agree with this opinion, or even that this is the best intellectual model to be using, but it's the one used in the tradition we're discussing, so it's what I wrote about.
2) Haven't seen anyone else lose it, but I've heard stories. These retreats are extremely challenging on every level: physically, psychologically, emotionally, and more. I recall watching a documentary about these retreats being implemented in prisons—one of the prisoners said, "This is the hardest thing I've ever done, and I've been on death row for 15 years." I felt pretty badass after hearing that!
I went on a whim, not really knowing what I was getting into. It was extremely difficult, and I suffered a lot, but it ended up being extremely positive for me.
I don't recommend doing this to everyone. From what I understand, the assistant teachers are trained to deal with people having psychotic breaks, but I don't know the extent of their training. I would imagine people predisposed to a break are those with deep unaddressed trauma, those not ready for an ego death experience, etc, though I am not a psychologist and cannot say for sure. I have heard stories of trauma being healed, as well as stories of it surfacing and causing a meltdown.
I am not a psychologist or a meditation teacher. I had a positive experience despite the difficulties, but I am just a guy on the Internet. Don't take my word as Gospel or do anything stupid. Your mind is powerful; don't abuse it.
Though my experience was a net positive, it's not for everyone. Serious shit has gone done at these centers:
https://www.womenofgrace.com/blog/?p=59797
3) Here is a link to the daily schedule, which I believe answers the question about retreat structure:
http://www.pali.dhamma.org/time-table
Goenka doesn't teach any walking meditation, unlike other Vipassana traditions. You can stretch during rest and meal periods, but Goenka is rather notorious for loooong hours of sitting. Meals follow the norm in monastic Theravada traditions, two meals in the morning and afternoon and tea in the evening. New Students (first-timers) are permitted a piece of fruit with evening tea.
4) I just want to make a couple more comments on the Goenka tradition, since I've typed up a shit ton already. Overall, my experience was extremely positive, even though it was fucking hard and painful as hell. I am grateful to the Goenka centers for having taught me emotional tools that I will be using for the rest of my life. I put a huge disclaimer above, but I think its net effect on the world is really good.
I doubt I will be sticking with this tradition long-term, as there is a thread of conservatism and puritanism that runs through the tradition. It's sort of an old-school traditional Vipassana school. IMO Goenka (seems to be overly confident that his technique is THE BEST, and has said some weird things regarding sex and celibacy in other interviews (not featured in the course). Cool if that's your thing, but it's just not my style.
I think the coolest thing about the Goenka centers is the economics of the whole thing. There's a worldwide network of hundreds of centers,
all 100% run by donations and volunteers. You are not allowed to give the organization money unless you have completed a ten day course. Literally the whole organization is just fueled by the generosity of meditators, which I think is pretty fucking awesome.
I am personally a big fan of meditation teachers Shinzen Young and Michael Taft. I highly recommend both of their books,
The Science of Enlightenment, and
The Mindful Geek. Here are a couple links; the second one can get you a PDF of
The Mindful Geek.
https://www.shinzen.org/
https://themindfulgeek.com/