  Reliable determination of Rotation-Activity Correlation (RAC's) depends on
precise measurements of the following stellar parameters: $T_{eff}$, parallax,
radius, metallicity, and rotational speed $v\sin i$. In this paper, our goal is
to focus on the determination of these parameters for a sample of K and M
dwarfs. In a future paper (Paper II), we will combine our rotational data with
activity data in order to construct RAC's.
  Here, we report on a determination of effective temperatures based on the
(R-I)$_C$ color from the calibrations of Mann et al. (2015) and Kenyon \&
Hartmann (1995) for four samples of late-K, dM2, dM3 and dM4 stars. We also
determine stellar parameters ($T_{eff}$, $log(g)$ and [M/H]) using the
PCA-based inversion technique for a sample of 105 late-K dwarfs. We compile all
effective temperatures from the literature for this sample. We determine
empirical radius-[M/H] correlations in our stellar samples. This allows us to
propose new effective temperatures, stellar radii, and metallicities for a
large sample of 612 late-K and M dwarfs. Our mean radii agree well with those
of Boyajian et al. (2012).
  We analyze HARPS and SOPHIE spectra of 105 late-K dwarfs, and have detected
$v\sin i$ in 92 stars. In combination with our previous $v\sin i$ measurements
in M and K dwarfs, we now derive $P/sin i$ measures for a sample of 418 K and M
dwarfs. We investigate the distributions of $P/sin i$ and we show that they are
different from one spectral sub-type to another at a 99.9\% confidence level.
