As stated, I think you have to have a strong support team to do both to the best of your ability. I Direct and DP but have a good Camera operator and Gaffer.
I definitely feel that operating the cam properly, especially during more complex camera moves, will interfere with your directing. It might not be by much but it will.
If your operating the camera, focusing on proper composition, following the actor, making sure the booms not in the shot etc. small nuances or performance flaws by the actors can go unnoticed. If your focusing too much on the actors the boom could dip into the shot for just a second or your pan might drag etc. Its just better to have someones complete attention on both of these jobs.
As far as lighting the most important part is to have access to the locations well in advance so you can plan and test your lighting ideas before you shoot. Bring your gaffer with you and make sure you are both on the same page and that he understands what you want. Use stand ins of the approximate height of your actors to dial in the lights. Once you have everything the way you want it draw a lighting diagram for each scene or setup and give a copy to your gaffer and relevant crew. Being thorough and organized is critical to pulling off both jobs.
Its a lot of work for just one person so you need to do as much as feasible during preproduction because once your actors arrive they are your primary responsibility.