Can I share files or folders with Basic/Plus users if I’m on a Business account?

Absolutely! As long as your team admin permits external sharing, you can share with any Dropbox user, even if they’re not a member of your Dropbox Business team. However, shared folder members who are not on your Business team will be limited by their own storage quotas. So while your team members will have more space to add and edit files in a shared folder, Dropbox Basic or Plus users will be restricted by their personal quota.