Yes, they are two different thing. One is for you to stay there and find jobs, while the other one is permit of working there.

As for the part-time job I mentioned, it is merely part-time to earn daily living expenses before I get my permanent job there. Before having the permanent job, I would just stay on the EPE cert until working permit given by my future permanent job employer (hopefully possible to find one in 6 months time)..

The immigration officer defines what is too much by going through your entry history. If they notice that you have been entering singapore too frequently without much 'cooling down' period, then they will chop something on your passbook, something like "Barred etc..."

BTW, all companies there have a quota of the number of foreign workers they can employ.