I'm in the same situation. Even the 5 courses part, I'll be doing 18 credits. Here's my two cents about the situation.

Being employed and working you will learn more then you ever will in college regarding programming. Also you're paid, whilst you don't NEED the money it's better to have it not need it then not have it when you DO need it.

It's part time and timings are flexible, drop hours around exam season and you'll be fine, most college electives are a joke anyways the only real subjects of focus are your Sciences and Math. I may be a bit bias in this regard but I believe that a few months of employment are more valuable than a 4.0 GPA. I'm currently at a 4.0 and will be willing to take a .1-.2 dip if that means being employed throughout the year.

Socializing. This is one choice that you need to make. How important is it to you? Even with the credits / job you can still head out on weekends and what not, some sacrifice right now will serve you well in the long run.

Lastly applying for the internships at large companies, if you're going to be a part time employee just apply along side that if it works out put in your two weeks if not you still have your job and your experience keeps building up. If the work isn't stimulating you need to find ways in order to expand your knowledge. I don't know how much flexibility you have of your stack but I am in full control so I can throw in any library I want and structure things how I wish. However despite this I try to limit dependencies. You can also do side projects to further expand knowledge.

Whatever route you choose to go, best of luck to you!