The limits I mentioned include both subsidized and unsubsidized federal loan programs. Any further amount you receive is either a private loan or PLUS. PLUS loans are made to the parent on behalf of the student, and actually were dischargeable by the parents' bankruptcy last I checked.
The graduate school limits are higher, but still exist. Med school students, for example, simply cannot fund their entire education through federal loans. The maximum period you can get through federal loans in any circumstance is around $140K, and medical school almost universally costs more than that.
It is possible to discharge student loans (not just Plus loans) in bankruptcy, but you have to basically prove that you can't survive while still making the payments. I don't know if it is easier to discharge the Plus loans or if they all require the same level of hardship.
Sure, but PLUS loans (for undergraduates) are obligations of the parent, not the student. The parent must agree to take out the loan and the parent signs the MPN.
The parent can, of course, take out unlimited amounts of money if their credit qualifies them to, just like they could by going to the bank themselves and asking for a loan.
The graduate school limits are higher, but still exist. Med school students, for example, simply cannot fund their entire education through federal loans. The maximum period you can get through federal loans in any circumstance is around $140K, and medical school almost universally costs more than that.