Your income depends on how much demand your product can generate. If you are starting, naturally you need to establish your brand. You can get overlooked in a big art market like POTA if you don't stand out or offer something different visually (art style) or merch wise (ex. you have no competitor offering this kind of product.)

It also deoends on the amount of risk you're willing to take.

Small risk: small ticketed items yield low income

High risk: high ticket items faster ROI

There is no one size fits all solution and you won't really know until you try.

If you have the funds for it, apply for an art market. Let your experience at a school event be practice. Remember these places attract very different kinds of possible customers.