Question – Hi I am an international student in the MS program

Hi, I am an international student in the MS program and applying for unpaid work.
Do I need to apply for the OPT that same as other international students who have a paid job?
What should my employer must do for me to have me as an volunteer at their practice?

Question – I am f- visa holder in the US have awarded

I am f-1 visa holder in the US; have awarded international students scholarship. I completed the first year of my two years graduate program. I was working as a teaching assistant in the University in last spring 2018. Now I’m doing my summer internship with CPT (Curriculum Practical Training). And, I just get married this month and I am thinking to file for adjustment of status. My questions are:
a. The I-485 form asks for employment history so do the on-campus teaching assistance and internship considered as employment?
b. If I file for adjustment of status now Can I continue working on the internship with the CPT?

Question – A student is current

A student is currently working on CPT which ends today. Their OPT does not start until July. Are they able to continue working as an unpaid intern/volunteer until their OPT becomes active?

Question – I got my F1 visa for

I got my F1 visa for a summer course at Dartmouth University, and I have been given 5 years although the course is just 4 weeks.
When I pursue MS in US next year from a different university, will i have to apply for a F1 again, or will an I-20 be enough?