This isn't a bad place to start asking these questions, but I agree with the above poster--you should supplement anything you learn here with the experiences of those who are actually out of school and living their career.
As far as this goes, medicine requires a sometimes-unbelievable amount of your time. For many it is incredibly intellectually satisfying and otherwise rewarding. That being said, it is still possible to enjoy a family life, but you will have to set boundaries from the beginning and decide what is really important to you. If anything physician-scientists are even busier that many doctors, because they are trying to balance two careers at the same time. To be a successful scientist, a physician-scientist must compete with MDs, PhDs and MD/PhDs that are 100% committed to research (many of whom either don't have families/outside lives or don't seem to care whether or not they spend any time with them). So, if you want to head your own lab, and see patients, you are only adding to the amount of time you will be spending on your work. But again, that really depends on where you set your limits. There is no ceiling to ambition in this field, and no one is going to tell you to work less.
However, if you can resist the urge to (try to) be the next Linus Pauling, you can see patients and work with another PI to satisfy your intellectual curiosity. And there is no guarantee that working harder or working more will lead to scientific success (though it does increase the odds).
Basically, don't consider medicine if you don't want to work. But don't write it off as impossible to maintain a life, either.
