No. They may be defined in terms of Metric units, but they aren't "based on" them. If they were based on them, they'd be a sensible integer (or decimal-factor) multiple of them, not some weird fractional measure. An inch being 25.4 millimeters may be the current definition of an inch, but that arbitrary length isn't based on anything in the metric world -- it's still just as based on the average length of the top joint of a medieval craftsman's thumb as it's always been.

Actually no, not for potential difference, current, resistance, impedance, luminosity, amount-ofsubstance …

For those you use the SI units.

Its just length, mass, (plus force and torque).

Not far to go.