2 DIFFERENT domains and active directories connected via VPN

Hi Guys,

I am new with the configuration of a complicated Domain Controller and Active Directory and I am seeking your assistance.

Legend:

• Our Company's Network = NETWORK A
• Client's Network = NETWORK B

Here is my current setup:

Our current setup is, we are accessing NETWORK B to connect to their application via RSA Token and there is NO VPN connection and NO Domain and Active Directory server it is just a workgroup configuration.

Here is my future plan setup:

I am planning to create a Domain Controller and Active Directory on a single physical server using Windows 2008 R2 Server. BUT I am planning to connect to NETWORK B using VPN plus the existing RSA Token and they have their own Domain Controller and Active Directory installed.  The goal to have VPN and our own Domain Controller and Active Directory is to control all our user registration and additional layer of security. 

MY QUESTIONS ARE:

1. Is there any conflict if we (NETWORK A) are going to Install and Configure our Domain Controller and Active Directory in NETWORK B?
2. Can we (NETWORK A) still access the application that we are currently accessing in NETWORK B?
3. Any issue with the security in accessing the existing application in NETWORK B?

Any suggestion or recommendation is highly appreciated.

Thank you in advance.