How To Prolong Internship Offer?

Currently scouting for Freshman internships and recently received offer for a brand-name Customer Resolutions job (not finance related). Part-time (20 hrs/week) & remote, so very flexible.  Beneficial for professional work experience, problem solving & relationship building, etc. I have questions I’d like insight on to optimize my summer & my resume.

1) Related to this internship, I received the offer today, but tbh it’s not ideal (in terms of resume / status) and I’m still in the process for recruiting for some other jobs that would be better suited for an IB resume (e.g. WSO internship, Big4 Consulting Internship, Regional brand-name insurance). The recruiter extended the offer today (without a response date), but I still have interviews for these better jobs. I want to postpone as long as possible and basically use this as a last resort, but I also don’t want to wind up empty handed. What can I say to the recruiter to respectfully allow myself to have more time to wait and see if I’ll be accepted to the other internships without saying this blatantly? Is it bad to email him that I need more time to make my decision and do I run a risk of losing the internship (is it even possible for him to take back his offer if I wait to long, how long would I have to wait for this to be a possibility?)

2) How should I best optimize my summer? Is something non-finance related like this better than just working as a barista/server and learning technicals on the side? Would it be smart to work as server, part-time internship, and grind through courses on the side?

Any insight would be great. Thank you so much.