What types of licences and quantity I need if I  plan to create below topology:

I have domain controler, which based on Windows Server 2008 Standard. This server got all Active Directory roles and I also have necessary quantity of CAL licences on them.

So:

I plan to add secondary domain controler which will be based on Windows Server 2012 R2 Standard. I plan to install on it Exchange 2013 Server Standard with roles: Mailbox Server ; Client Access Server; Unified Messaging Server; Hub Transport Server. Exchange user will be around 30.

What is more I wanna secure this server by creating in my network third server with Windows Server 2012 R2 Standard which will have Exchange edge transport role and will be in DMZ zone. Do you think this is good idea , or how can I do it by using another method?

So summarizing:

1st Server 2008 Standard is now DC (i have necessary CAL licenses)

2nd Server = Windows 2012 R2 Standard (will be secondary domain controler with the same roles as 1st Server). Exchange installation with roles: Mailbox Server ; Client Access Server; Unified Messaging Server; Hub Transport .

3rd Server = Windows 2012 R2 Standard (server will not be in domain, DMZ zone). Exchange Edge Transport role.

What types of licences I need for 2nd and 3rd Server ?

Nobody participating in these forums is qualified to quote licensing terms on behalf of Microsoft.  Please contact your Microsoft representative or reseller, and/or check out the Microsoft Exchange licensing page:

http://www.microsoft.com/licensing/contact-us.aspx