How difficult/challenging should the mock papers be for the students?
I want to obviously challenge the students to ensure they are learning but I dont want them getting false hope from doing an easy mock paper. What is the best paper to take?
I have not covered all topics to date to give the students a choice of questions in their mock paper and for the short questions they will only be able to answer 3/5.
Have you covered most of the syllabus by the time your students will sit their mocks?
Ok, you have a list of requirements for the paper, so the easy answer to your problem is to make up your own paper! You can still give them a choice (of sorts) by putting a number of questions on for each topic and let them choose which one(s) to do. Put the same total number of questions on the paper so that they experience an exam which is the same length as the exam in June. You could use past LC exam papers as a guide the designing the questions. You are not under any obligation to use papers provided by third parties. There's nothing to stop you making up your own paper - I did it many times, especiually when, like you, I was not finished the course.