"Am very ambitious and feel a need to be highly successful at whatever I do. Without career fulfilment I become too obsessed with trying to mould my children into perfect little beings, which can't be good..."
PG, I am a 10+ yrs PQE solicitor and I agree with a huge amount of the advice on here, given by people with direct experience of every part of the coal face. My tuppence ha'penny is to look at what you say from the perspective of your statement above. The fact is that no matter how well you do in the GDL and how good an understanding of the law you require, you are unlikely to feel remotely "successful" for at least 5 years PQE ( so 9 year from now!) because that's how long it takes to have any level of confidence in what you are doing. That's all very well when you start off as a new trainee/pupil in your first job but to go back to being a rookie when you have been in a position where you are trusted by parents and other teachers, have the confidence to stand up in front of a class or an assembly and know what to say and how to say it, where children look up to you as an inspiration and a guiding force in their lives, where more junior colleagues seek your advice....
I can say with all honesty that being a trainee is crap, two years of not being allowed (or knowing how) to speak directly to clients would be mind-numbing at your stage of professional life. Being a junior lawyer is in my experience like doing an endless stream of essays for a highly critical but disinterested teacher - don't expect hours and hours of patient teaching and discussion when you get it wrong, which you invariably will just becuase he/she has a different style to you. Nobody taking you seriously without "partner" on your business card, having to cc a partner on every single thing that you send out (this is not egomania on their part by the way, it's required by their insurers).
And if you do get into court, know that (even at a more senior level) about 65% of what you will be talking about is procedural technicalities, admissibility of evidence, adjournments, disclosure, why document X has to be added to Bundle D at new tab 16B, all under the steely gaze of a judge whose sole aim is to make you feel as stupid as possible - very little erudite debate about the substantive legal and factual issues. You can see that for yourself in the mini pupillages though, just try not to get too rose-tinted.
As others have suggested, you must have a high degree of ability, experience and maturity in teaching, looking at the posts on here there are a lot of people who are crying out for better quality people to whom they can entrust their children's education, there are advocacy opportunities on panels and things - if it's success you want then going back to the beginning is the last way to attain that.
As a final word, if you do get on vac schemes with law firms, my experience of having vac students is that it's very very hard to find any work for them which accurately replicates what it is really like doing the job, so my advice would be to use it as a good way of making contacts and to capitalise on your relative maturity by getting some of the 5-6 pqe solicitors out to lunch and grilling them about what they actually do. And one thing they might tell you is this - timesheets. A total and utter bloody nightmare. Think VERY VERY hard before embarking an any career that requires you to record every single thing that you do all day in 6 minute units. If vac students were required to fill them in then the number of applicants for TCs would halve, I guarantee it.
Good luck with your decision.