Some very good advice from Beska on this thread so far.
Going back to your first point about making a decision - By all means get some work experience together now and see how you're feeling about it. Talk to anyone who'll listen and get all the opinion good and bad (But don't let anyone make your mind up, no matter how much they insist). You're right in saying it is a lifestyle choice and massive commitment so make sure you understand it and you're in the right frame of mind when you start. If you aren't ready or aren't sure, there's nothing wrong with that at all. Many of the best doctors and medical students I know didn't come to it till they were past 25, for one reason or another. The thing being, its easier to take another career route or degree at 18 and switch into medicine rather than the other way round, for a whole world of reasons (The most practical one being a debt burden designed around a high-earning career ladder).
If it comes to UCAS application day and you think you'd rather have a more normal time at university for three years, study something for the enjoyment of it and then come back to medicine in your twenties when you might have a better head for it, then I would wholeheartedly recommend that.