Whats the best approach for on camera acting?
I can not answer that simply. Best advice would be to get int a good scene study class or on camera class and work work work.

Do you enjoy theater or on camera acting?
I love mixing it up. Both are great and have there own challenges. I enjoy the immediacy of theatre and the complete journey from begging to end every night you perform. With film I find it exciting to go to a new location or set. Film is great because it lasts forever. For both film and theatre I find collaboration fulfilling. I like being part of a team.

Is there a big difference between an agent or manager? Do I need one or both?
Well you need one or the other, yes. These days a great manager can be as good as an agent. I like to have both because then I have more resources to get jobs. Also your relationship with your manager and agent tend to differ. An agent typically has more clients and is not as available for the day to day strategy of your career. Whereas a managers typically is. It really is a matter of personal preference for the actor.