Apple_Boot partition created on external drive?
You created one HFS partition, and one Core Storage partition, on which an HFS partition resides. The difference is that a Core Storage partition can be encrypted. I've never found a use for the Apple_Boot partition, although it is replaced with the recovery partition when you install OS X. You needn't worry about running out of partitions. The limit is ridiculously high these days. The EFI partition is part of the GUID Partition Table format by default, and should be kept. Neither Apple_Boot nor EFI take up much space, so I'd shy away from deleting them without a good reason.