1) Probably because its a number of months between interview and completing the TR so they don't know the exact requirements. It is easier for them to offer you a base when you can get there and start flying quickly.
2) no idea
3) Check the website but I think that you need to do a winter season with them
3,500 hours total flying time, a minimum of 2,000 hours on a JAR25 aircraft i.e. a Multi-crew, Multi-engine aircraft with an established airline and a minimum of 800 hours (Pilot in Command) PIC on a medium jet aircraft >20,000kg and 500 hours PIC on the B737-300 to 900
Thats for Direct entry so I would imagin that the upgrade would be similar maybe slightly less.
Nick