0patch Agent takes approximately 4 MB of disk space in the installation folder, mostly for its executables.
Logs in %ProgramData% should take a negligible amount of space unless debug logging is enabled, in which case the 0patchLoaded.log will grow quickly. (However, due to a bug that we're fixing in the next release, sometimes logs can consume a lot of space, in which case you can use the cleanup script described in this article.)
The Updates folder under %ProgramData% stores downloaded installers for updating the agent (typically 3 MB each).
All micropatches are currently stored in the registry (yes, they are that small), and along with other data stored there they consume approximately 280 KB of Registry space (which translates to similar-sized disk space consumption.)