is it manageable?

Obviously, otherwise nobody would complete the degree. I don't really know what you mean by this question...

Otherwise, you get paid basically minimum wage to work 40+ hours a week doing very difficult, often stressful work.

Is it worth doing?

It's worth doing if you need a PhD, otherwise it's not worth doing. From the sounds of it, you don't need one. Doing a PhD when you don't need one is a waste of time, energy, money and can even damage your health - both mental and physical.

Do you have much of a social life outside of the lab?

I had very little social life outside AND inside the lab. A PhD is a very isolating experience. Not necessarily because you don't have time to socialise, but simply that there is nobody around to socialise with. All of my PhD colleagues were too busy with their own shit to care about socialising, and basically just had their own social circles to bother hanging out with me (fuckers). Outside of work, I never really met anyone. Moving between shitty rented flats doesn't give you much opportunity to build a rapport with neighbours - if they are even decent people to begin with, which they might not be.

Also, going out clubbing etc. to meet people, while not impossible, is just... not really what PhDs tend to do. You'll probably spend your down time relaxing after a hard day's work, or catch up on reading papers, instead of going nuts in a club.