iTerm2 does not show username, machine name, time
Everything you're asking has more to do with the shell than with iTerm. There are numerous tutorials on how to set up your PROMPT variable (I use a modified version of this one). Since you're using Oh-my-zsh, try looking through the themes page. There are a variety of styles available (I began with the af-magic prompt). Once you find a prompt you like, feel free to copy the source from the .oh-my-zsh/themes folder to .oh-my-zsh/custom/themes and modify the custom version. Details on custom plugins and themes are available here.