Depending on the substance, you're most likely facing felony charges. As a first offender, you may be eligible for a diversion program or othe alternative. Yes, you need a lawyer.
The above answer is for general information only and is based on the information you posted. Every case is fact dependent, so to get a thorough analysis of your situation, you will need to consult face to face with an attorney licensed to practice in the jurisdiction where the incident took place. Do not conclusively rely on any information posted online when deciding what to do about your case.
Yes, absolutely! You cannot plead under PC1000 it's an aggravated felony and even though you won't be convicted, for immigration purposes you will be convicted. A lot of criminal defense attorneys don't know this. Feel free to give me a call with any questions.