The HIFLUGCS sample is a complete sample of nearby massive clusters. High-quality multiwavelength data are available. Here, we present results on X-ray--optical correlations, including X-ray luminosity, temperature, gas mass and total mass, all based on several Ms of Chandra and XMM-Newton data; BCG magnitude and stellar velocity dispersion, and cluster galaxy velocity dispersion using a median of 185 member galaxies per cluster. The extension of some of the relations into the group regime is discussed based on an X-ray selected group sample. A brief update on temperature profiles in the very cluster outskirts as determined with Suzaku is given and some prospects are shown for constraining primordial non-Gaussianity with eROSITA.