A star forest is a collection of vertex-disjoint trees of depth at most 1, and its size is the number of leaves in all its components. A spanning star forest of a given graph G is a spanning subgraph of G that is also a star forest. The spanning star forest problem (SSF for short) [14] is to find the maximum-size spanning star forest of a given graph. In this paper, we study several variants of SSF, obtaining first or improved approximation and hardness results in all settings as shown below.