If your phone is rooted you can use TitanuimBackup to backup individual Apps.If you want to have a full backup using a rooted phone then just use CWM or TWRP Recovery to make nandroid backup.
If you're running a stock firmware , you can try backing it up using ADB. There's a tutorial on here teaching you how to do so : http://forum.xda-developers.com/show....php?t=1420351
And to Factory Reset your phone follow these steps :
If the phone is working you can simply find it in the settings.
If your phone isn't working then :
Turn your phone off , or just pull the battery out and put it back on.
2-Simultaneously press Volume Up, Home ,Power button
3-When Samsung logo appears , release the Power button.
4-Use the volume buttons to to choose Factory Reset/Wipe Data and choose it by clicking the home button
Please press the Thanks button if i helped !