1. In general: $\ce{acid + H2O <=> base + H_3O^+}$
2. It is called the Henderson-Hasselbalch equation
$\ce{pH} = \mathrm{p}K_\mathrm{a} + \log\frac{\ce{[base]}}{\ce{[acid]}}$
3. I believe the equilibrium constant for a such a neutralisation would look like $K_n = K_\mathrm{a}K_\mathrm{b}\frac{1}{K_\mathrm{w}}$