Mgiration from 3.1 to 4.0

Hi,

Can anyone please help me to know,

We have more than 2000 reports to migrate, during migration from prod 3.1  to dev 4.1 will that distrub the prod environment ?

is it necssarry to migrate user security along with users and groups  or can we do it manually in the dev 4.1 once we migrate users and groups.

Thanks,

Pavana