GUI Final Scene/ Item Pickup

My intent with the project that I'm doing is to have the player pick up a bunch of items and then have a GUI overlay that uses an image sequence in the GUI played very slowly as a makeshift cutscene. Probably not the most efficient way of doing things, but its what I came up with. Problem is, other than making items that the player is able to pick up (via colliders) and making a script to make an image sequence in the GUI, I don't know where to start. I guess my ultimate questions are:

How do I represent items picked up in a GUI and update it so that it plays an image sequence once all the items are picked up? (apologies if that isn't coherent at all)