Should I form an LLC and a Trademark?

I am a personal trainer that is thinking about starting my own mobile personal training business. I would like to know if I should register for an LLC? (I live in Maryland) And I have a motto that I would like to trademark. What is the benefit of forming an LLC? And should I trademark my motto? Because it's something unique and haven't been used before. I am new to doing business by myself. Any help or pointers would be greatly appreciated.