When does nucleophilic attack and proton transfer happen?
Because you are a beginner to organic chemistry, I'll tell you this: Both esterification (e.g., Fischer esterification) and de-esterification reactions are reversible. The question you had at the end is why the last step of base catalyzed de-esterification reaction is only forward reaction. As you have learned in general chemistry class, acid-base reaction is one of the fastest reactions in chemistry (not counting nuclear reactions). Thus, the last step is governed by preference for acid base reactions:

$$\ce{R-COOH + OH- -&gt; R-CO2- + H2O}$$

The $\mathrm{p}K_\mathrm{a}$ of $\ce{R-COOH}$ is about $4.7$ ($\mathrm{p}K_\mathrm{a}$ of $\ce{CH3-COOH}$ is $4.75$) while $\mathrm{p}K_\mathrm{a}$ of $\ce{H2O}$ is $15.7$. Therefore, forward reaction is about $10^{10}$ times faster than backward reaction. 

Also remember, this reaction is in aqueous medium, therefore there are much more $\ce{H2O}$ molecule available than $\ce{R-OH}$ molecules. Thus, going back to ester reaction is much slower than becoming acid (governed by Le Chatelier principle).