G Suite by Google - This one is 100% essential and we recommend it to everyone we work with (and if we work together, we'll absolutely get you set up on it!). This is a great baseline tool for your email, document sharing, calendar, and all sorts of great collaboration tools. Just do it, trust us.
FreshBooks - We're obsessed with FreshBooks, and have been using it since the company started back in the early 2000s. It's great cloud accounting software for startups (and frankly for any business) and will save you a tremendous amount of time in ways you couldn't even imagine. They're the best, and they'll make your accounting super easy.
WordPress + WP Engine - If you're building a content network, look no further (in our opinion). If WordPress is good enough for the New York Times, it's probably good enough to at least get you started.
Envato Market - If you're looking for some great shortcuts as your build out your content network, this is a great place to start. Stick with the well respected developers and themes, and you'll be in good hands.