Just going to address some points that have been missed above:
"Also, I'm in year 12 and doing 6 subjects, so I kinda want to do the UCAT but also scared that it would affect my other studies, so what do you guys think? does UCAT prep affect school subjects?"
Yes and no. It depends on how you structure things. If you find yourself needing to allocate time to study UCAT that was previously going to be used for your school subjects or vice versa, then it probably is affecting your school subjects. I'm yet to see evidence that under proper organisation, UCAT prep affects school performance. It's probably also important to keep enough free time for yourself too, to prevent burnout.
" Also, how many hours a week do you recommend practicing UCAT?"
It depends. You can ask for as many recommendations as you like and if you got explicit answers like 5 hours or whatever I honestly think that's poor advice (or at least, you wouldn't get the same figure every time). It really depends on however much you need. The one thing I will say on this is to try not to study more than you need to because at the end of the day it is an aptitude test, and much like anything else there are diminishing returns past a certain amount of work (you're best off doing something you need / like to do instead), except I personally think the drop-off, in this case, is a lot larger. This question gets asked an abnormal amount and I don't think my answer has changed at all over the 2.5 years since I did UCAT.
Trust your own ability and do your own prep, you'll do great!
And yeah, pretty much this.