Is it just me, or are stories of ten years preparation like serious overkill? If I entered year 7 half expected to get an Oxford offer, the majority of my school years would have been of varying amounts of pressure and having to work hard, instead of being care free and coasting, which they were. If you need that much preparation, are you really enough of a 'free thinker' to go to Oxford, really? Plus, preparation and getting in arent causal. There is still a majority chance you dont get in. Therefore, structuring your entire, or at least the latter years, of secondary/sixth form education around applying/getting into Oxford and then getting the knockback is just setting yourself up for depression. I'd never even considered the place till the end of my AS's when I realised I was pwning all my subjects and went down there to see how beautiful Oxford was.
On that HAT point, its never that hard. Hearing the subject matter being '12th century Iceland' makes you think its really hard but that's just a title. The other bit was on the communist revolution in Vietnam, which I equally knew nothing about, but the sources tell you what happened and fairly blatently convey what themes there are. The key is just clear, analytical writing. All the stuff is written in english, you can understand it, its not going to be that incomprehensible. Its just about spotting themes or chains of causality, the subject matter itself barely comes into it.