The answers to a lot of these questions depend on you, and it's certainly better to be asking yourself now than later.
I'm going to echo Dermviser for the most part.
A lot of people have a relatively easy time in m1/2...as long as you're efficient and organized, you'll probably be one of them. You'll still be in class/studying a ton, but it's not the end of the world. If you enjoy biology as a general rule, you will probably also enjoy m1/2 (though there will be low points where you wish you had never seen a textbook).
M3 will suck, based on all accounts. However, even m3 will probably have some easier rotations. They aren't all surgery. M4 is a better balance, but mostly on the second half of the year.
Internship/residency vary hugely by specialty.
My personal advice: don't write off medicine because of the hard work upfront. It's certainly possible to "marry your profession" here, but many do not. Entire specialties have relatively low hours: anesthesiology, derm, opthalmology, psych, PM&R, radiology, Emergency (although calling it a "lifestyle" specialty is debatable), etc.
You aren't alone in feeling the way you do. Many of these specialties are competitive because they offer a good lifestyle. Medicine does not require you to marry your job.
Having said that, understand that many doctors feel it does: therefore, when you mention lifestyle, they'll treat you like you're "cheating" on medicine.
Good luck!