On the one hand, this type of organizational structure benefits from having individuals entirely dedicated to one function. In some cases, there can be cost savings and efficiency gains in combining functions in this way. However, this type of organizational structure is prone to conflict.
The alpha subunit (RpoA) initiates RNAP assembly by dimerising to form a platform on which the beta subunits can interact. The alpha subunit consists of a N-terminal domain (NTD) and a C-terminal domain (CTD), connected by a short linker.
DNA Polymerase is a polymerase that synthesizes a DNA strand ... so it's used in DNA replication. RNA Polymerase is not used to form the primer-that is primases job. RNA Pol is used during transcription to synthesize the mRNA strand. EK does a decent job describing a primer.