  [Abridged] We present Gemini-N GMOS-IFU observations of the central starburst
clumps and inner wind of M82, together with WIYN DensePak IFU observations of
the inner 2x0.9kpc of the disk. These cover the emission lines of H$\alpha$,
[NII], [SII], and [SIII]. We were able to accurately decompose the emission
line profiles into multiple narrow components (FWHM~30-130kms) superimposed on
a broad (FWHM 150-350kms) feature. This paper is the first of a series
examining the optical structure of M82's disk and inner wind; here we focus on
the ionized gaseous and stellar dynamics and present maps of the relevant
emission line properties.
  Our observations show that ionized gas in the starburst core of M82 is
dynamically complex. Localised line splitting of up to 100kms in the narrow
component is associated with expanding shells of compressed, cool, photoionized
gas. We have been able to associate some of this inner-wind gas with a distinct
outflow channel characterised by its dynamics and gas density patterns, and we
discuss the consequences of this discovery in terms of the developing wind
outflow.
  The broad optical emission line component is observed to become increasingly
important moving outward along the outflow channel, and in general with
increasing height above/below the plane. Following our recent work on the
origins of this component, we associate it with turbulent gas in wind-clump
interface layers and hence sites of mass loading, meaning that the turbulent
mixing of cooler gas into the outflowing hot gas must become increasingly
important with height, and provides powerful direct evidence for the existence
of mass-loading over a large, spatially extended area.
