I have strong knowledge of HTML, HTML5, CSS, CSS3, PHP, MySQL, jQuery, Javascript, Ajax.
I have done previous projects that included parts of your requirements (order management for ERP system based on calendar use, inter office message board that uses calendar and clock modules etc.).
There are issues to be clarified like: design, UI for integration of displayed content (probably div or iframe), authority management etc. However, everything is doable within the right time frame and money budget.
I use to work only with pure language, no dev environment in order to control the scalability, integration and bug propagation.
I am sure I can build for you perfectly.
Thank you.