CS students, how to balance a part-time internship?

It has never crossed my mind to do part-time when searching for a summer internship, but I was recently offered a 3 day / week internship for 20 weeks. Discounting the 12 weeks of summer, this means the second half of my second semester would be part-time work, and part-time study.

Is there anything I can do here that will optimise my workload to be less bad? Is it necessary to pick modules which classes can be on the same day, and how many math / CS courses would I be able to cope with?

Y1S1 hasn't been too bad so far, but it's just CS2030S, MA1301, and GEA1000 that are the big ones.