Upgrade 11i (11.5.10.2) to R12 (12.1.3)

Hi all,
I have to start to upgrade EBS from 11.5.10.2 to 12.1.1 then to 12.1.3 on linux 5 Operating System in Test instance.

1) What is difference between upgrade & migration activities will do in r12?
2) Do we must to upgrade the DB to 11g as the Oracle desupport issue or want to reduce downtime?
2) Do I need apply 11i.AD.I.7 and 11.ATG_PF.H.Rup7 patches first?
3) And do I need to convert the application/DB to Multiple Organizations before upgrade? Any guideline?

Please suggest me, how to start?

Thanks,
Ajay