I feel like I can reply here given I'm in a similar situation as you. I'm starting undergrad this fall and like you have been pondering what I should and should not start in regards to preparing a competitive application for the future. To be straightforward, I don't believe you have to "juggle it all" in the sense that it doesn't have to happen all at once.
I like to think of the main pillars of an application to be GPA, MCAT, research, clinical experience, and non clinical volunteering primarily. Just as important would be hobbies and leadership activities, and you should therefore be planning your activities around having experiences in those categories. That should answer your dilemma about what to do as a premed.
I can't really answer for you how to do the activities because the way people get access to opportunities is unique to each person, but you most definitely don't need to do it all at the same time if you start early, which you seem to be eager to do since you're posting this question. The way I'm structuring my activities is mainly to do ECs during summers and leave the school year to focus on work and preserve a good GPA. Remember, ECs aren't going anywhere and a gap year is always an option to build those. A low GPA is much harder to fix and will require more than a gap year, so prioritize keeping the GPA high, then do the ECs.
With that said, I'm not saying don't do any ECs at all freshman year. I'm doing ECs myself, but the point is to keep it light. Starting early puts you in a position to put forth just a few hours a week and still gain a large number of hours because you can do it over multiple years. In my case, I've been doing some shadowing and food pantry volunteering which is taking up maybe 10 hours a week, and that is quite light, but it adds up over time. During the school year, I intend to continue the food pantry work and drop the shadowing, while starting some volunteer work at a hospital. Again, it sounds like a lot, but its not, because I don't have to put in more than 6-10 hours a week since I know the hours will grow if I do it over 4 years.
Lastly, I'll address how I'm going about research. For this, I leveraged my research experience from HS and emailed professors at my school who do research in similar fields or topics and used that alignment in interest to get lab positions. If you haven't done prior research, you can still absolutely express interest in the topics a professor is researching and show why you'd be a good fit for a lab that way. Additionally, since these type of research positions will be at your college, it will work around class timings and schoolwork.
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