That depends whether you have more than 4 GB's of data saved or plan on getting that much data.
Yes. Saving xbox game data works almost exactly the same way as saving xbox 360 game data.
no the xbox cant
20 gb
about 45 KB/s
Its great for people who dont play Xbox that much. However, a 4 gig wont hold much data so you wont be able to download much addons and demos.
$100-$150
No, I do not think this is possible. Plus, I'm sure it would corrupt the data that is the original one for account b and then use account a's Xbox Live data. Not only this, I know it's impossible to have save-data and other stuff used on another account when it's account a's information.
you can link the servers of the ps3 to xbox 1 and transfer data.
at the most $200
no the hardrive you plug into your xbox 360 can only be used to play music, films and pictures from the hardrive on your xbox 360 you can not play any games nor store any xbox 360 data on the hardrive.
have saved ironman data on your Xbox 360 or ps3