Experienced dev here working on fleshing out a brand and service targeting a local niche with my wife.

Say I want to use an off the shelf tool where a non-tech person can flesh out and theme a website on a custom domain. This person would be able to log in and draft blog posts/calendar events/e-commerce products from an admin type of UI. This tool would also allow customers to create accounts to interact with this site. This tool would also be able to connect to and use data from a 3rd party API that would be deployed and developed independently by myself.
I can build the service portion quickly, BUT… 1) I want my wife to manage content/marketing/branding independently through a UI, 2) I want to offload user management/servicing/permissions, and 3) I want to easily connect to and display data from my custom web API.

What tools have you all had success with?