1. The tools that are given to the agent are almost the same to the one defined in Opencode, except for Skills and Subagents (both features not implemented in zerostack)
2. Zerostack is prompt-based, so that it ships with a set of .md files, stored in ~/.config/zerostack/prompt, and that can be selected from the TUI in order to activate different 'agents': as you can see from the README, it is designed to contain the most important feautres of superpower + Claude's front-end design + git worktree support and Ralph Wiggum loops (both as integrated features)
2. As said before, there are no benchmarks right now, but it is good enough for me, so I hope it's good enough for y'all :)
3. Transfering settings from other agents is out-of-scope for a minimalstic coding agent, but the idea is that, apart from MCP server, the rest might just force you to learn how zerostack works, because of design choices such as not having Skills or having certain specialized tools integrated (worktrees and loops).