Ok. So as I understand your question:
You would like to find an internship, however you are concerned about what you could possibly contribute to an experienced CPA practice. Also, you are wondering how you would communicate with them and sell yourself as a potential employee or intern.
And here is my perspective:
The CPA office would determine how you could help. In general it'll be grunt level work. Copying, clerk stuff, sorting, greeting clients. Things like that. But by being at the office you can push yourself to try and help with more value added work. Perhaps even do some research for the CPA if asked. Or you might even do some research on your own for something you know that they haven't researched yet and give them a report on your own time with links to the rules and websites and all that. (For example, say there was a new rule that just came out or that a client is doing something that impacts them in another state that the CPA hadn't worked with before, you could research the information on your own and provide a report in email with website links on where the CPA can find the information to do their own analysis. This saves them time and it allows you to learn how to do something and it gives you feedback on what you're doing. Or you might learn how to do Excel and help them with some bookkeeping work. A reconciliation if they feel comfortable with you. Things like that which an evolve over time as they begin to trust you and you show you can do those things. (By the way, this isn't normal for the average college student but there is nothing to say you can't do it. Just don't he arrogant. LeBron and Kobe went straight to the NBA. There is not rule that an 18 year old can't do Excel reconciliations or tax research)
As for how to get a job or internship: A letter written directly to CPA practices in your local area asking for an internship, opportunity to work, or informational interview could work. (Research each CPA you write to and include a note specific to them in one line or paragraph.) I would put together a form letter about yourself. That you are a local student and want to gain practical experience while in school. That you are passionate about accounting and are motivated to learn as much as you can. That you work hard and are willing to do what is necessary to contribute. That you would love to either work for them part time, intern, or do an informational interview. (Even if you get a job, I would still try to do an informational interview with them. I would also formally thank them and also send them a holiday card every year or birthday greeting to keep in touch. Or some sort of update on your career with a note on how they helped you and thanking them. Things like that to keep the relationship and network.)
Include a resume or bio in your letter. It doesn't have to be a formal resume but just highlights on you. What you're doing. Interested in. Etc.
Send both the resume and letter l to your professor beforehand and ask for his or her feedback or advice. Make sure to try and make it easy to read. Make it well organized. Use bullet points and bold. Get feedback from business writing expert you know...or something like that. And try to make the letter no more than a 5 minute read...and something that can be skimmed over quick in a minute if necessary. Like say if you wrote a letter that could be read in 5 minutes...maybe bold some of the key words that get to the point. College student. Love accounting. Work part-time or internship. Informational interview. (Also build relationships with other professors you can find.)
If you can find a person that knows someone that works in accounting do an informational interview with them. If you know someone at the CPA practice then reference them in your note or letter...or if you know someone that knows someone....etc
Expand to other places you can work. Perhaps the college has an accounting department you can help work at part time. Perhaps a local bookkeeper needs help.
As for what you can do at a CPA office. Filing. Copying. Receptionist. Coffee. You might be able to research for them (Like research something obscure that they haven't got to yet and then give it to them in a summary form as you understand it with links so that they save time)
You are not going to be the one to make a decision on the treatment (that is up to the CPA to determine), but if you can save the CPA hours of research during a busy season that is valuable. And obviously it is valuable to you because you learn things at a higher level. (Also, before you give the research to the CPA you can go to a place like r/accounting, r/tax, r/taxpros, r/bookkeeping, etc to either research the question or ask others if your understanding is correct. (This will provide additional confidence to yourself that what you are providing is value added...but remember you're the student and they are the teacher...and even if you believe they may misunderstand something it's not your decision. They have the credential and it's their license and they have others in their personal network they rely on and they know the specifics of the situation with the client.)
Remember in sales each 'no' gets you one step closer to a 'yes'. And all you need is one 'yes' to get a job or internship at a company.
As for business and investing, I would focus more on really diving deep into accounting. Maybe read something like Accounting For Dummies. Read those books and websites I referenced. While investing and business are tangential, what guy really need to learn is accounting. Both the theory and practice. You might even watch lectures on accounting or take an online class on the side for fun at Coursea. I believe they are still free (It's a way to learn from top institutions while you are doing other things and move ahead on the learning curve while you have free time)
UPenn is a top school...lots of wealthy students and successful students.
Illinois is probably fine as well
Spend time taking Coursea courses on the side when you're not busy with other stuff. (In my mind you should try to get to the point where you're ahead of the other students in class because you are so comfortable with the meterial that you can work ahead and learn new concepts)
While investing is tangential to accounting, it is not accounting (It is something that you can learn in the future after school pretty easily or taking classes at uper division levels at University). The same goes for 'business.' The better you learn accounting and more quickly the better opportunities that come along because people will understand that you can speak intelligently on the subject and understand a lot of concepts / rules.
Okay...well that's a lot. Sorry it isn't organized...but I had to put this down and pick it up a couple of times.
P.S. - Here is a link to another comment I made with additional links in it. I think they are good to read the threads for others ideas and my opinions on these things.