As I mentioned in another comment, the Goenka courses actually easily accommodate up to 9 hours of continuous sleep at night, from 9:30PM to 6:30AM. The pre-breakfast meditation is encouraged, but entirely optional. You could even nap for another hour after breakfast. There's also an hour to hour and a half of nap time after lunch.
I personally get 8-10.5 hours of sleep a day when doing a Goenka course. I go to bed at 9:30, have an alarm that wakes me up at 5:30, nap after breakfast from 7 to 8 and nap again after lunch from 11:30 to 1PM.
Just to add to Luke_Grecki's comment (which is spot on), at some of the old student courses it's not even mentioned. The Goenka centers are remarkably passive about donations.
I've been doing Vipassana via Goenka for over 10 years, have gone to courses at a few of the NA centers, have done a satipatthana sutta course and other shorter old student courses. I can confirm the comments by Luke_Grecki and eternaltourist.
There is no big secret behind how they are run. It's exactly the same whether you are just starting it or have been doing it forever. There's no pressure to donate. They mention it at the end of each 10 day course and that's pretty much it. At some of the short old student courses they don't even bring it up at all.
The centers are safe, the people volunteering are there to make sure your basic needs are met so you can meditiate without distraction. The centers are run by normal people who volunteer. The center trust meetings I've attended are just like practical, run of the mill board meetings.
Regarding the specific concerns, you can actually sleep up to 9 hours easily if you skip the sittings before breakfast. The first required sitting is after breakfast. The sleep thing is really a non-issue. When I'm at a course, I pretty consistently sleep a full 8 hours from 9:30 to 5:30.
The assistant teachers are mostly there to try to nudge you in the right direction. All you are doing is focusing on breath or body sensation, so there simply isn't much to teach outside of goenka's instructions. It's more a matter of just doing it. I suspect that some people have difficultly with the lack of human interaction and try to use the assistant teachers as an outlet for it, but it's counterproductive since it breaks deep concentration and distracts the mind.
As for leaving, eternaltourist's comments are spot on.
In my experience, anapana is more difficult and brings up more stuff because, unlike vipassana, simply focusing on the breath doesn't provide a way to deal with the stuff that comes up.
The thing to remember, though, is that you are trying to focus on breath (anapana) and body sensation (vipassana). Specific thoughts are more or less a distraction. Of course, your thoughts and mental state are tied to the sensations you experience, but because staying equanimous to the sensations is the tool your are using, the actual content of the thoughts are not something you are trying to focus on.