Installing FreeBSD from USB or the CD/DVD is an extremely fast. You only need to choose UFS or ZFS for the disk type. I would suggest using mirrors if using ZFS. After install is done, all the system admins needs to do is configure the IP, setup root, and add other usrs. It is recommended to add yourself to the list of users since ssh over root will not work by default. This is done for security reasons.
As for securing a dedicated server, the greatest security edge is that the operating system doesn’t come with a lot of preinstalled software. This prevents hackers from using exploits to gain access. As admins, you are only installing components that are required and it is much easier to maintain few components on a server.
The operating system itself has several security features such as different secure levels. Secure levels locks down the system and prevents any unauthorized changes. For example, it will prevent firewall rule from being modified once they are in place. Thus preventing any authorized user from making changes.
FreeBSD also comes with framework which allows programs to lower their permission when they need it. The program that allows this is capsicum and it is very handy tool when it comes to server security.