planets with ammonia-water oceans

I wanted to ask a whole series of related questions about ammonia-
water oceans on other celestial bodies, so please bear with me: First,
is an ammonia-water mixture better for life in general than pure
ammonia? But probably not as good as pure water? (I know that in the
universe, H2O is far more common than NH3.)

Is a planet with high atmospheric pressure and or bigger than Earth
necessary to keep ammonia part of the H2O/NH3 mix? Or a higher
percentage of NH3?

Will a CO2 atmosphere always break down the NH3 much more than the
H2O? If so, is that why there is or may be more NH3 on outer planets
and their moons than on inner planets like Earth? And could there be
other sorts of atmospheres where the ammonia-water mixtures can thrive
without both NH3 and H2O breaking down en masse, like a hydrogen-
nitrogen atmosphere?

In answering all these questions, what would be the differences
between oceans, rivers, and so on that would be 5% NH3 and 95% H2O?
How about 10% NH3, or 15% NH3, or 20% NH3, or 25% NH3, or 33% NH3? (I
know that each of those ratios has drastically different melting and
boiling points.)

In fact, would NH3/H2O ratios change over periods of time, e.g. one
day to the next or one week to the next?

A final question: if Earth and Mars reversed in their orbits so that
Earth rotated in Mars' actual orbit, would there be a slight
percentage of NH3 in the water, so that the melting point would be
lower than is the case here on this Earth?
.