An external drive will function like an internal drive in most cases. I use a little of each. I find that 1 large hard drive is easier for me to manage, but I have about 6 different drives, and I get confused easily!
Partitioning the drive into two (or more) "logical discs" might be handy though for different computers and their data. You're not locked in though, and can redo it at any time. (although you will lose your data)
Are you familiar with the "Manage" command that is available when right-clicking on "My Computer?" Look for disk management to see your drives and partitions.