mate Navigator Carrier with Antimicrobial Protection,

Is there one or two locks on the door? Is this the most durable one from Precision?

Is there an opening through the top as pictured?

Can one add castors to roll the crate easily and safely if need be? If so, what castors are recommended?

Is this crate collapsible (so I can transport it when visiting family and then use it when we arrive)? Thanks.