Firstly, the CPE is widely regarded as being tough, but you're right it doesn't cover the same amount as a normal three-year law degree - it is limited to the core subjects as set by the law society.
There are several two-year courses that offer the core subjects in a similar way to the CPE, but offer students scope to take a few extra modules, perhaps to reflect a specialism that the student is interested in. My own university offers such a scheme, and its very popular. It counts as a qualifying law degree in its own right and is not classed as a CPE course. It is however, only open to graduates.
Part time work is possible, however I only know people who work on weekends... It all depends on your own personal time management skills... There are people who seem to manage everything. I worked in a bar for one night a week in first year and didn't find it to be a problem - as I said, you'll need to sort out your own study timetable.
However, I've since given that job up due to study pressures and work full-time during the summer months, but I do accept that I work too hard during term-time, and perhaps could get away with doing less work. However, I also have a 71% average with one 81% mark this year which I feel that I could not have achieved without putting in some serious hours...
See how things stand during your first year, and then make a decision on employment. If you want/need it, you'll be able to fit it in and the same goes for sporting and society activities. I wouldn't worry - you'll need something to take your mind off law.
And as for Oxbridge - I have never been to Oxbridge, but have heard the horror stories. What I can say is that I have several friends who could quite easily have gotten into Oxbrige - they have spectacular grades, come from the right school/social backgrounds etc - and they (and me) all find law at Queen's to be bloody hard... I can't imagine Oxbridge being much harder that what we do.
However, there are two things that I should point out. The first is that we all work very hard, perhaps too hard, but get the grades that reflect this. I expect that we could get by with less work and still get where we want to go. I would imagine the Oxbridge tutorial system would force students to work hard all the time rather than it being a matter of personal choice. The second is that the Oxbridge terms are shorter so there is more work crammed in to a shorter time. So in that sense it may well be harder. Oxbridge students do seem to be able to fit in a huge amound of extraciricular activities though - I always wonder how they manage that.
At the other end of the spectrum there are universities that do offer an easier degree. In my neck of the woods there is the University of Ulster whose law degree is a complete waste of time. Yet again I can qualify this by saying that when it comes to get onto our version of the LPC, UU students tend to do better in the entrance exam (you have to get in on merit - there are very few places). Our LPC exam requires no specific legal knowledge (indeed, if you mention cases etc you actually lose markes) and the UU law degree, while in no sense of the word academic, is quite practical in nature. This seems to offer UU students an adavantage, however I've heard that for the Bar exam and at the top end of the spectrum Queen's students do better.
Does being less academic make the course easier? I'd have to say it does...