Activity type for different companies

Dear Experts

  In my business scenario we have 7  different companies with different  manufacturing process

    we have finalized to capture the below overhead through the activity type  among the group

Machine Hour

Setup hour

Maintance hour

Each and every company rates are different   here my doubt is

1. 1.Shall I have the Activity types  company wise or  common activites

2The  activity type unit of measurement  is HR, suppose if I do the production confirmation as MIN future am I going to face any problem

Could you please give your inputs

Thanks & Regards

Sri