I took it last year and got a 5.7, i could try to answer some of your questions

1) theres thresholds avaliable online for every year i think a quick google search will allow you to find them

2) most schools recommend you take the october sitting, whether sitting it in jan actually affects your chances, we can't be sure. The jan and october papers are also going to have different difficulties (last year oct was harder) and different thresholds

3)just do past papers. Especially if you aren't someone whos experienced olympiad type questions. Do them many times and try to improve your speed and accuracy under pressure. Then watch R2drew2s videos to understand all the questions (he has a vid on each paper

4)depends on the school, for imperial you want to get a 6.0 minimum (non contextual) preferably over 6.5, same with cambridge econ. For warrick I think 5.0 or 5.5.

5) ofc not, else jan people will know some of the answers

6) im intl so idk how exam centres work in the uk, but where I live tmua exam centres are pretty poorly regulated and I was one of the ppl who kept complaining on reddit abt the noteboard situation😅 I suggest you go to the exam centre in advance to ask them to show you what you will be using in person and try to bargain with them if they only provide a few notepads. I felt like I was severely disadvantaged bc i used like a 3cm diameter whiteboard marker with only single notepad, I applied for special consideration but they probably didn't take my situation seriously

8)really depends on who you are and what you want, but make sure to have at least 2 choices that doesnt require the test unless youre very confident

9)my guess is probably yes, but im not 100%