Theft and Larceny: Theft

I'm at the age of 16 and i got arrested for stealing. I did it with 3 of my friends and stole from people in our school. We got a court date and a public defender. We are being charged with 4 felonies of grand theft. We are for sure that 2 of those were not above 400$.

I wanted to know who we should tell this information to. My public defender also told me about getting recommedation letters from my teachers. Would that help? I'm thinking of doing some community service to kind of pay back for the crimes I did. Would that help me at court at all? What is probably the sentence i will receive? What is the worst and best case scenario. Also my defender said something about only admitting to one of the charges, what does she mean by this?
Thanks in advance.