I was last employed in 2012 and had been a full-time housewife since then. This year (2016),I started conducting a seminar part-time in the state university. I only conduct the seminar about once every 3 months. The expected total income for the year is minimal, likely less than my personal exemption. As of now, I do not expect to engage in any other businesses. The university withheld 10% of payment for withholding tax and 3% for percentage tax. (I am still questioning the 10% classification).

1. Do I need to register as a self-employed individual given this frequency of engagement?
2. Am I required to register as a business in DTI / my municipality?
3. If I do need to register, can this type of work to be categorized as WI120 (individual contractor with 2% withholding tax)?

Would appreciate some advice. Thanks!