What is the best way to create a simple OS for PC Tech game?

By OS I just mean an operating system of some sort. An example of game play would be:

The game is a top-down view controlling the PC Tech character. He can run around a building talking to people and doing things but at some point he will need to go back to his computer and check things. When the players clicks on his specific computer it will transition to a new ‘scene’ or area that is the operating system I mentioned. So, now the mouse controls the cursor and the player must click a logon button to get into the computer. Once that happens, it loads a ‘desktop’ with clickable shortcuts. Additionally, I want to implement a timer system that will randomly pop-up emails or instant messages (or even help tickets) that gives the player a task to complete. What I’m lost on is how to get started with the Operating System. I am using a full screen widget blueprint at the moment which pops up a new screen when clicking on the Tech’s computer but it doesn’t seem like it will be granular enough to handle the other things I mentioned.