Sounds like you're actually looking for something pretty complex if it needs all of those features. We use Asana for managing remote teams and that's worked well for us. If it needs to be something that lives inside GMail, maybe check out Streak. It's a lightweight CRM that let's you manage different processes, flows and relationships from within your inbox.
Hey there - founder of streak here. We use Streak internally to manage our product development process and bugs pipelines. We even have a blog post about how to use streak for that. See blog.streak.com. happtly to help if you need, reach me at aleem at streak.
