How do you describe your working experience? A great and clear explanation can portray vivid image vis-a-vis to your potential and capability to the employers. The clearer the explanation, the higher chance for you to be selected. 

1. Do you need to state "full time" or "part-time" on the working experience section?

You are only allowed not to state "full-time" or permanent position on the working experience section. Hence, it is mandatory for you to state other working experience statuses such as internships, part-time, self-employed and contracts. 

2. "I have worked in professional field for 3 years and resign from the job to continue my studies for 4 years. That being the case, is my experience still counted or considered in the working industry even if it has exceeded 5 years?"

We recommend you to insert it all in the resume or perhaps create a cv. The experience is clearly vital hence it needs to be stated especially if the past working experience is directly correlated to the applied job/ within the job scope that is applied for. 

3. "Let say if the part-time job doesn't relate to the field that we desire to apply, is it still valid for us to put it in the resume?"

Absolutely! You can describe all the aspects of the position as transferrable skills.