Am not sure which you are asking about:
Jet2 do not currently fly to Dublin so one can not fly from Leeds to Dublin with them. They have flights from Leeds to Cork and Belfast but not to Dublin.
No direct flight to Dublin
no
Yes.
The ID that is needed to fly to Dublin from Prestwick on a Ryanair flight is a passport.
You need your identification documents and fare to fly to Dublin from Prestwick on a Ryan Air Ticket.
none
no you dont
go to your local airport and fly there
It is cheaper to fly from London to Dublin than to rent a car in London and drive (and catch a ferry across the Irish sea) to Dublin. If you shop around you can get some very good value air fairs from London to Dublin.
You could fly. You could get a bus to Limerick and from there get a bus or train to Dublin. You could drive.
Charter flights do operate from Dublin to Cancun and reverse for holiday makers.