Regarding prac exams, just focus on Legal. Don't worry about the 1/2s. I probably did about one or two practise exams for each of my year 11 subjects in the lead up to the exams, they were in class though and not timed.
Don't do practise exams either until you have finished the course. Aim to do this by the end of term three. As you go along, I would suggest you read over the material studied in class in the evening and ensure you keep up to date. As others have mentioned, it's a good idea to get a hold of Checkpoints (they're cheap, but your school library should have copies too), do the chapter revision questions to entrench what you are studying into memory.
The only exception may be English if you wanted to get a head start for Year 12. I wouldn't worry about though until later on in the year when you know your books and understand a structure for Language Analysis/Context. A tutor would be handy here, who has had experience with the current course.
For my 3/4 last year I did about 5 or 6 full practise exams and the remainder I just jotted down brief dot point responses. For some subjects, there are only a certain amount of questions that can be asked so you find that you are just repeating responses but tweaking wording slightly to suit the q.
Remember its only year 11, enjoy the year in preperation for Year 12.