It seems doable. You may not have a lot of free time for the semester, but it’s only a semester. Internships can be very helpful to landing other jobs in the future.
Add up all your work time, including commute time. Estimate how much reading and homework your other classes might have. See if there is still time left to eat, sleep, do laundry, have fun, etc.
So working 30 hours would be 3 credits for the internship?
For a regular class, you take 3 hours in class, and you are expected to have 2-3 hours of homework/studying per class hour. So that would be 9-12 hours of work a week per 3 credit class. 30 hours a week is like two to three 3 credit classes.
So adding on 3 additional classes seems too much…2 classes seems better. And how will you fit them in with the 30 hours/week?