I can't really answer the first one, as military history is not my forte. But the second one I can do!

Efforts of collectivization predate the Great Leap Forward, which officially started in 1958. As collectivization progressed, encroachment on peasant household interests increased, and with that, villagers attempted to withdraw from collectives, much to the disapproval of the government. (Note: a collective is not the same as a people's commune. A people's commune is much larger than a collective, and on average consisted of over 5000 households.) Villagers would demand to withdraw from collectives, petition the government to allow them to withdraw, attack cadres, seize the means of production (e.g. tools, seeds, livestock, oil, fodder, grain) from the collective to redistribute them among individual members, and otherwise disrupt entire production teams. The government insisted that very few people wished to withdraw and that disturbances were caused by those of "bad class backgrounds", and ordered cadres to hold mass debates and meetings to educate them on socialism (and otherwise single out those who were labeled 'counterrevolutionaries' and 'landlords' and 'people with bad class backgrounds'). Eventually the villagers resigned themselves to collectivization, which allowed the people's communes to be formed.

During the Great Leap Forward, significant opposition didn't really occur. After all, people were pretty damned hungry and couldn't bury their dead, let alone rise up to beat up officials and whatnot. Furthermore, people who did try to speak out could be and were subjected to beatings and physical torture. Nevertheless, there were some grassroot officials who realized how dire the situation was and tried to rectify it. The most notable of these occurred in Sichuan Provence, as there was a trend amongst grassroot cadres to allocate land to households, allocate output quotas to households, and disband communal kitchens. Although officials were replaced, the countercurrent could not be stopped, helping to save lives.