Hi,
you dont need an invitatoion for an Open day but Emirates does recommend to send an online application as it is the easiest way for them to hget bacl to you later etc.
You only need the last mentioned files only if you are successful for final interview! Than you would need one further fulllenght photo in business attire and one causal photo, 4 passport sized photograpgh, passport copies and if you are selected to relocate to Dubai you will have to take 24 more passport photos in sky blue!!! and I also had to bring 2 reference letters with me but some posted that they do not require them anymore so it is better for you to prepare them anyhow.........
last but not least my inbox is no empty and ready to welcome other messages:-) CU