That depends on how they (the court) interpret intent and "compensation". The concept "noncommercial" is explained by CC thus:
NonCommercial means not primarily intended for or directed towards
commercial advantage or monetary compensation.
The actual license language in the US BY NC license says
You may not exercise any of the rights granted to You in Section 3
above in any manner that is primarily intended for or directed toward
commercial advantage or private monetary compensation.
If we just stop there, then a reasonable interpretation of "a manner that is primarily intended for..." is that the possibility of receiving money is not the primary intent (which is e.g. "making this service available to others"), but it is a possibility. Additionally, a donation is a gift (meaning that it is optional), thus it is not owed (wages or liability payments are owed, in contrast). However, the IRS considers a gift from an employer to an employee to be compensation. On the third hand, the IRS does not consider all gifts to be compensation, and on the fourth hand the IRS gets to interpret words in a special way for tax purposes, which don't determine other interpretations of "compensation". A couple of legal dictionaries identify an American English usage "salary of wages" (not the case here), or it refers you to "remuneration; that which is given in recompense". Black's 2nd pocket refers you back to compensation but also "payment". A "payment" is (Blacks, again) "Performance of an obligation by the delivery of money or some other valuable thing accepted in partial or full discharge of the obligation" and "The money or other valuable thing so delivered in satisfaction of an obligation". What distinguishes a gift from a payment is the obligation: there is no obligation to donate. Donations are consistent with the above limitation.
Just because the entire clause would (in case of legal dispute) be in evidence, the rest of the clause says:
The exchange of the Work for other copyrighted works by means of
digital file-sharing or otherwise shall not be considered to be
intended for or directed toward commercial advantage or private
monetary compensation, provided there is no payment of any monetary
compensation in connection with the exchange of copyrighted works.
That means that there can be compensation (meaning "something obligatory in consideration of), as long as it is in the form of digital files.
The next question is whether item 2 – advantages contingent on making a donation – changes anything. You can get free cloud storage from Dropbox: but if you make a certain level of donation to them, you get more storage and features. This is not in fact a donation (and they don't call it one), it is a payment for something that they would not otherwise provide. I would not go so far as to say that rewarding donors with something special automatically turns a donation into a payment, but I think it would be on the edge of the ice to claim that a set of advantages contingent on making a donation is still a "donation". I don't know if there is any case law (not bound up with tax consequences of "donations") that answers this.
The third option is straightforward: offering CC NC material for free does not prohibit also offering non-CC material for pay on the same website. It may be necessary to structure the pages so that users do not incorrectly infer that donation is mandatory to access the free stuff.
