Try real hard to beat the rap, spending money on a top lawyer might pay off in the long run. If you are convicted, get it expunged. I assume it's not intent to sell? If so you are hosed.
You will have to report a conviction to the FAA when you renew your medical.
A misdemeanor should not be a problem for the TSA background check, but the airlines may ask about it. The airlines also have some access to FBI records. The FBI will probably not expunge anything from their records, they are not subject to local law, so assume that the airlines might find out about it anyway. If you lie and they find out later, you will be fired and will be finished in the airline industry.
Assuming you have a couple years of college, and then flight instruction, it may be five years before you apply to a regional. That is probably about how long they would like to see elapsed. DO NOT get in any more trouble, not even a speeding ticket. The fact taht you are young and have time on your hands will help, but do not establish a trend.
Be aware that when hiring resumes, they will have a long list of qualified applicants with a clean record, so you will probably be at a disadvantage until they use up the waiting list.
In the past this would not have hurt in the long run, airline people understand youthful indiscretions (once). But due to the colgan accident congress has told the airlines to crack down on their hiring standards. Nobody knows exactly what this means yet, congress left the details up to the airlines. Maybe they will focus on pilot qualifications and experience, but they might also look more closely at criminal and financial records. Since you have not invested much in flight training, you might want to pay attention to the industry and the new rules before you commit a bunch of time and money. Nobody knows where this is headed just yet.
If you really want to be a pro pilot, stay away from drugs and drug users...they just do not mix at all. You're going to get tested regularly as a pilot, so you may as well start practicing now.