International awards. No, it's not good enough. All student awards are not counted. However, they might be mentioned by some references or they may be used to strengthen the contribution. No. The award should be international, or at least at some national level. Multiple national awards in multiple countries are good to use.
I don't know the answer, and here's what I saw online. http://www.kenzl.com/node/7 It seems that if this conference is in a specific field, then this award may not be enough to meet the criteria. But if this conference is a general one , probably okay. However, the safest way nowadays is to claim the strongest 3 claims, and use all others for totality. The two-part petition is what the IOs are looking for. http://www.uscis.gov/USCIS/Laws/Memoranda/i-140-evidence-pm-600