I have had similar concerns about the workload, but not so much anymore. I've seen many stories online of people who have made the part-time programs work, which have been comforting (links to which might be comforting for you, but alas I am of no help). I have also talked to a couple of people who have made it work, and it seems to be very hectic early on, but then they learn to deal with it. One of the people I talked to about this trains pilots for Delta (and therefore has to fly a small part of the year as well), and he made it work. My assumption (valid or not) is that if I can keep full-time work to just 40 hours most weeks, I should be fine. Having perhaps one night off during the week and the whole weekend to take care of studying seems like enough for a part-time schedule, but perhaps I am naive.
As far as the job prospects, I am less certain. I actually have many questions about this (many of which I expect to direct towards the career center at the school I end up going to). If you go full-time, then it becomes fairly obvious that you would use your summers to either get summer associate positions or other intern jobs. If you plan on working all 4 years you're going part-time, that doesn't seem very likely, and further, I wonder if it is more difficult to even get summer positions without being part of a traditional full-time class.
Now for some better news on that front. I work at a moderate size law firm in the south (400 attorneys), and we just hired someone out of Georgetown's part-time program, so it does happen. There are also other ways of getting work experience (and thus likely job opportunities down the road). If I end up going the IP route, I will pursue become a patent agent, which would at least have some relation to a future legal career.
Anyway. Good luck.