Do the NGO Internship. Helps to have that sort of volunteering experience when you apply for Masters abroad. If you intern at a firm or chamber in your first year, you won't be allotted much work and you'd spend your time observing proceedings or reading cases. You will have lots of opportunities to do that in your later internships. But at an NGO there'd be no dearth of work, and you would learnt to interact and negotiate with various stakeholders, which is a major soft skill. Most law related certificate courses are a sham, so don't go down that path.

You can apply. It’s unlikely without connections because for profit folks don’t usually want to invest time and money teaching first years.

Certificate course and all is useless. Write a paper instead. What’s wrong with spending some time at NGOs anyway? I learnt a lot when working with them.