I am a huge user of Linux in a all kinds of ways for servers, desktops, etc...
More recently I am wanting to try working with FreeBSD for certain features it has like ZFS and such.
How much does the administration of a FreeBSD box vary from that of a Linux box? Such as package management, device management, network configuration, etc...
Somewhat of a subjective question, so it kinda depends on your perspective. Package management, device management, network config and similar things are all done with different commands. But the concepts are the same. You have packages (usually), you install them, etc. You have networks, you connect do them. Conceptually, not that much different. Practically, very different. But most of it is pretty easy to pick up and well documented in the FreeBSD Handbook. Best I can say is give it a try and let us know if you have more specific questions.
Both have their advantages and disadvantages. A lot of people will probably tell you it boils down to one-system architecture (*bsd) versus the distribution-system of the various GNU/Linux distros. For a good in-depth analysis of the various differences, look at BSD For Linux Users
Personally, after using OpenBSD and FreeBSD for many years, I've grown to like their way of doing things, for example the ports tree. But recently I've come across some snags in the BSD way. If you want to live on the edge and use really new software (not versions, I'm talking new stuff that haven't got a huge following yet or is more niche) then a GNU/Linux distro is easier to get working of the bat. At least in my experience anyway. I'm certain you can find BOFHs that disagree ;)
Basically, if you want bleeding-edge, Linux is a better platform to go for, and it's pretty stable as well, even Ubuntu Unity's gotten really nice in 13.04, from the perspective of a guy who uses the Unity spin of that distro with his hardware currently and really digs it.
However BSD's been in the game for a bit longer, and has a smaller, more mature and close-knit community than Linux, and they emphasize more on the maturity and stability of their OS as far as packages go as well, however the downside to BSD is it's a bit harder to use if you're used to some form of Linux as you have to compile most stuff in it, however you can install from packages in it too, in that way, Linux isn't much different as in some distros, ie. Gentoo or LFS, you have to compile everything from source, in distros like Arch, you can either compile from source or install from binaries, meanwhile distros like Ubuntu, Fedora, or Debian get their stuff mostly from binaries.
However there are desktop-oriented forms of BSD out there, most notably PC-BSD, which take a similar approach to Ubuntu in that they make BSD as easy to use as possible, and as accessible as possible to people that are new to the platform
Ultimately though, it's just a matter of preference, I for example, prefer Linux for the focus on having the newest stuff, and 'cause I'm accustomed to it the most, specifically Ubuntu or Debian-type distros, while others may prefer BSD for the stability of the packages.
