Data migration

Experts,

I am trying to use import wizard BOE XI 3.1 to export to BIAR file and import it with UMT in BI 4.1. I want to do it incrementally. What is the best way to achieve this.

Should we move users & groups first and than later move the folders? Or If I decide to move users, groups and one folder at a time. Do I have to import the users, groups second time as well when the second folder is being imported?

Can I use UMT in 4.1 and do Live to Live migration from BOE XI 3.1?

Thanks in advance