Hi, I would like to know more about the octopus card, can you please help me with this?

Regarding the Airport Express Tourist Octopus:

1) What is the different between one free single journey and two single journey?
2) for the 3 days unlimited travel on MTR, izzit only applicable for MTR route? will it be available for other transportation charges such as buses?
3) for the stored value, will it be deducted within the 3 days unlimited travel or it is only be use after the 3 days usage?
4) The deposit of $50 will be refund to me right? where can I get the refund? can i get it in HKIA on the day that i'm leaving hk?
5) for this type of octopus card, izzit once i use for the 1st time, it will be automatically become unlimited for the coming 2 days? or I can use it whichever date i like as long as for 3 days?

Other than this Airport Express Tourist Octopus, izzit there is another tourist octopus card that cost $55 for the one day unlimited usage? if yes, this card only available for MTR route but not other transportation such as buses?

I'm not very clear about these, can you please help me out? Thanks