How can they force you not to choose a subject? Pretty sure its your choice. Remember, teachers end up as teachers because they weren't the best back then.
yes, they are absurdly difficult incomparison to actual hsc questions. Don't waste your time doing them unless you want a band 3. If you hate MIF, you probably are garbage at math but there's no one to blame but yourself if you fail.
Maybe not. The 8th mark in a 300th school is probably 60%, so you will take home part of the 60% hsc score from that person if he got the same marks as in trials.