At the moment I am not sure if the post office is still there due to rennovations happening there. Last I checked it is still there.
In May I ordered some overseas money online and I was to pick it up at my chosen post office.
I went there and the line was small and the process was fast, all I had to do was to show my identification to staff.
It all depends on the time of day you go with how busy it gets.
I have bought stamps and asked questions in the past. With it being in a smaller shopping centre, it isn't extremely busy there.