When do I need a civil engineer?

If you are asking this question, then the short answer is when someone requires it. The best way to find out is to look at the requirements for your proposal or to ask your town if your plan requires an Engineer to sign off.

when do I need a land surveyor?

A Licensed Professional Land Surveyor (PLS) is necessary for anything dependent on a property line.

If you need to submit a plan showing how far new construction will be from your property line, you will need that plan signed by a PLS.