Answering “amein” should not be done in a voice louder than the the one making the beracha. (The same din applies to answering barchu or even birkas hazimun.) If the intention is to encourage others to join in (in answering amein or the other responses), one may do so.
Chazal permitted one learning in a Beis Medrash to eat or drink there, something ordinarily forbidden to do. This ,however, is only to facilitate the learning , or to avoid bittul Torah. Otherwise it remains ossur. If, for example, one is learning somewhere in the morning, and plans on leaving after that morning seder, he may not, after that seder, eat his lunch in the Beis Medrash or drink a coffee there.