The couple of social media management tools best suited for a start up are:
-Hootsuite: It is a powerful tool that helps you track all your social media channels in one place. You can see who is talking about you, engage with them, and measure your performance.
-Buffer: It is a simple tool that lets you schedule and publish content to your social media channels. This way, you can keep your followers engaged even when you're busy.
Both Hootsuite and Buffer offer free plans that should be sufficient for a start-up.