Does anyone know where I can set the alpha transparency on an entire object that has several different materials assigned to the mesh?
Seems I can’t remember this.
Thanks in advance!! 
What you could do is create a node group that accepts one input, the last shader noodle in each material (the one that would previosuly gone into the material surface slot) inside that node group you have a mix shader and a transparent node into the bottom mix slot. You share this node group with all of the materials on the mesh, and you keyframe the mix factor by right clicking on it, so 1.00 would be fully transparent.