Exchange 2003 to Exchange 2013

Dear Expert,

I need your consult  from customer question below.

                Customer has used Exchange 2003, they have a problem from increasing user. They have the idea to implement the Exchange 2013. But they don’t want to quit the old version because their cost policy.

                Another pain point, they have used MS. Outlook 2003, they know outlook 2003 cannot work together with Exchange 2013.

I need you to help

1.       What’s the different Ex 2003 and Ex 2013?Benefit?Screenshot? How to migrate?
2.       Why Outlook 2003 cannot work with Ex2013? Why outlook 2013 is better?
3.       Pros and Cons to upgrade to Ex2013, what’s the customer should prepare.

Thanks in advance.