Agglomerative Clustering without knowing number of clusters
A minimum cluster size will not generally be satisfiable in hierarchical clustering. Instead, you have to expect many clusters with just a single point.

ELKI has some fairly interesting techniques to cut a dendrogram. Check the clustering.hierarchical.extraction (or so) package. If I remember correctly, some allow you to set a minimum size (but there will be a "noise" cluster with all the leftovers).