Convert a Template to a Website

I’m looking to use an OpenSource calendar software to create pre-set calendars (such as sporting events, religious holidays, etc.). I would like to then sell subscriptions to this calendar service to businesses/organizations, allowing them to display designated calendar(s) on their websites. In some cases, customers may subscribe to more than one calendar. The display should still be a single calendar with all events shown (perhaps color coded) and a drop down menu that allows filtering (to view individual calendars at a time). I will need the ability to add/update events on my own and/or import events from other sources. I would like a quote on evaluating OpenSource calendar alternatives and identifying which would be the best fit, setting up the infrastructure on a server for managing the calendar, creating a GUI for me to add events, creating a method for me to generate code to subscribers, etc.