Agreed, time management is key! I am sure you know this from undergrad, but it is especially important to keep in mind in grad school.
Also I think that if you are doing the program full time then it will be hard to work full time. I know people who did it, but they did not have a life outside of work and school...not saying that even if you do work part time and do school full or part time that you will feel like you have a life, but at least you won't have AS limited time to get things done. Either way, that is why having EXCELLENT time management skills is essential!
I personally, went to school part time and worked basically full time hours (but was able to have a flexible schedule). It was tough and mentally draining, but well worth it.
Congrats to you and good luck in your studies!!!