Don't Buy Office 2013
Microsoft's business is more and more reliant upon Office and, with the release of its most recent version it has changed its licensing terms to make this a product that home users should avoid like the plague.
Retail copies of 2013 will be locked to the first PC that they are activated on. Replacing your PC will also necessitate the purchase of another Office license.
I suspect that Microsoft's reasons for doing this are to encourage the take up of its Office 365 online suite. Getting you to pay monthly forever works out to be a more profitable model for Microsoft and they'd like you to help them restore their business by doing so.
Having evaluated Office and Office 365 for several enterprise organisations in the past I strongly urge you to look elsewhere for your productivity software.
If you are happy with an online solution then Google has an excellent solution in its Google apps suite. Otherwise I suggest you run Open Office which is free and a very close fair match for Microsoft's package.
Combining the two would give you the best of both worlds.
Whilst most enterprises will struggle to move away from their dependence on Microsoft Office you shouldn't allow yourself to get sucked into doing the same.