NT1330
HOMEWORK
Active Directory Design Scenario
To effectively achieve this I need to know and understand everything about Active Directory Domain Services.
When designing and implementing an Active Directory domain, you need to think about the placement of your global catalog servers. The global catalog is the master index of objects within an Active Directory forest. The global catalog serves as a quick search tool to locate objects within a forest. Every domain must have at least one global catalog server. The first domain controller (DC) installed into a domain automatically serves as that domain's global catalog server by default. As the size of your forest grows, there may become a need to configure additional global catalog servers throughout the forest. There are two main issues to consider when placing global catalog servers into a domain. The first is the traffic levels and the second is the location of infrastructure servers.
As the forest gets larger, so does the global catalog. As the global catalog expands, the amount of replication traffic it generates increases. Global catalog servers replicate with each other. This is separate replication traffic from that used to support Active Directory itself. From an overall perspective of the forest, when fewer global catalog servers are deployed in a forest, there will be less replication traffic, but it will cause more query traffic. Conversely, deploying more global catalog servers in a forest will cause more replication traffic, but reduce query traffic. Replication traffic can also be managed.
As for the number of DCs it would depend on the number of servers the company will have and which would work as Client/Server.
And for the recommended method for the OU design it will follow
Domain>Application>computer>Client/Server.

Company Merger Scenario
Since the only information from the other company is that it has a directory service, I would consider to merge the other company into our functional-level AD DS Forest.
For the compatibility I would have to update all the old operating systems to a Windows server 2008 because the company Active Directory only works with Windows Server 2008.
Considering trust relationships will come along during the merge taking in account that we will have more information about the new company.