The minimum number of hours for getting a teaching work permit/ARC is 15.
I’m not sure what “benefits” you are referring to.
Your employer is obliged to pay national health insurance contributions for you, as well as payments to some kind of employee protection fund IIRC.
But as far as I am aware, the statutory paid holiday requirements do not apply unless you recieve a fixed salary. If your pay is based on the hours you work, whether or not you are paid monthly, you are not salaried and hence not entitled to paid holiday, or any holidays for that matter apart from national ones. (This is how I understand the law only and in no way represents definitive legal advice!) Anyway, as the statutory paid holiday only starts accruing after a year without paid holiday you may not be missing out on much.
Was it holiday benefits you were talking about or other ones? If you are referring to discretionary benefits (i.e. ones that your employer chooses to provide; their provision is not compelled by law), then you may be out of luck. I don’t believe that you can force your employer to pay you the same as other employees.
There is a minimum annual wage figure of around 48,000NT but it may to apply to non-teaching work permits only;
[Minimum salary for ARC and tax?
[ARC and "Required Hours"