The use of liquid detergents is recommended over powders in washing machines as they do leave a mud build up over time in the bottom of the wash bowl
no they do have to be dissolved before use
spin speeds are set in the machine program and cannot be altered
spin time is set in the machine program and cannot be altered
use the recommended detergents for the machine because if you use top loader detergent in a front loader it will froth up excessively and cause problems for a front loader machine
the suitability of use for the detergent ( powder or liquid) is clearly marked on the labelling on the bottle or packet