Masters

Firstly, you need to have a Bachelor's degree. Then, you have to meet eligibility criteria for admission in New Zealand colleges that include English proficiency scores, Bachelors grades, resume, Statement of Purpose, Recommendation letter.

Yes, you can do PG from any country, remember to meet all the eligibility criteria of the college you want to apply for admission.

Yes, you can get admission in PG Diploma or MA course according to your interest. you are eligible for both.
Good luck.

Yes, you are eligible for this subject, you can apply for the admission.

Hey,
You're eligible for the same.
However, as far as the salary and scope is concerned, so the professional psychologists with M.Phil and Ph.D degree earn quite handsomely and those engaged in private practice have more scope for earnings. In this field, your starting salary can vary between INR 1.79 LPA to INR 6.23 LPA.

According to my knowledge, you should do MBA, from there you will get good opportunities for your career.

Yes, it's a good option if you are serious about your future then go for it. It's a good return for your future if you done it from any good University. If you want you can also choose for MBA it's also good.