Functional questions Managing Marketpress

We've got a multiple site marketpress installation running.
And there is a customer who wants the following :
1 : User/Customer pool in all webshops. So if one buys/registers he can access all webshops
2 : Ordernumbers should have upfollowing numbers in all shops, so if you get ordernumber 1 in shop a you should get ordernumber 2 in shop b with the first next order.
3 : VAT should be decided per product

Is this possible?

Thanks in advance