DAZ Studio is a separate free program that is similar to Poser but does things differently.  It is a matter of how comfortable you feel working with DS and whether it is beneficial to use both DS and Poser or just use one program.  Of course, both programs have strengths and weaknesses.  

To address your situation, I would recommend downloading the DAZ Install Manager (DIM) which is also free from DAZ3D.  Although this program has a bit of a learning curve, it is your best option to install DAZ products into both DAZ Studio and Poser without attempting a manual install from their compressed files.  The Victoria 4 base package that you purchased contains both DAZ and Poser installations, you need to identify which files are designated for which program.  That is why I suggest DIM for installation unless you are very confident with working with zipped files.

What is the product that you purchased?  And BTW, V4 base is sometimes offered as a weekly freebie, you would have to be patient but it does appear every once in a great while.