I have a multi-entry ED visa, anyone know how leaving the country and coming back works?

I have a multi-entry ED visa from a university in Thailand.

I have plans to visit home this summer and come back to Thailand to continue my studies.

I thought it was as easy as just flying and coming back since I have the multi entry visa….. (good through December).

A friend of mine was saying that no, I need a bunch of paperwork from the school saying I have permission to leave and come back and like some kind of authorization letter or something…. Is this true?

Also, another question… How long can I be out of the country for? What are the steps to leaving and coming back in? Sound I expect any sort of questioning by the officer?