I earn around $1000 a month as a part time private tutor for the past year and intends to apply for SIRS, but i have questions on filing income tax?

1) I have not made any cpf/tax declaration before. As my annual income doesn’t exceed $21000, what contributions do I have to make after filling income tax?

2) If i declare myself as self employed, is the status reversible as I’m currently a student intending to pursue an employment in the future?

3) Lastly, will the self employed status affect considerations for subsidies and bursaries as I am currently on financial aid?

Thank you!