build a website that is easy to update and integrates with cloud based backend platforms

I am updating my website [login to view URL] which was build using iWeb. I hear that wordpress is a great and inexpensive content management system. Would like to integrate to mailchimp and capsule (crm). Internally we are using xero and podio and i want all these backend systems be integrated e.g i don't want to manually update contacts in any of these systems. The second phase of this project will include building a ecommerce site i am looking a magenta go, but have also heard that other systems would be great. I want a bid on phase 1 of this project. Kind Regards Gitte