AYou have a number of rights. First of all you must make them aware of your dyslexia. I assume that the college is aware of this, in which case they should be able to offer specific help such as access to technology that may help you. There is no reason why the school, if the college asks, should not vary your timetable.
There is no minimum number of classes you should teach. It is a judgment for the college and school to make. You have to show that you can teach whole classes over a sustained period. Many colleges have guides to the percentage of teaching, but how this is defined will vary. You have to spend 120 days in school - that is the only figure.
Anyone with dyslexia, any other form of learning difficulty or anyone with a physical disability should read Able to Teach, the latest guidance from the Teacher Training Agency (available on its website) and contact the equal opportunities officer and occupational health professional at their college or workplace. They can access extra funding and help to ensure that reasonable adjustments are made to ensure that you are not discriminated against.
The latest legislation to cover you is the Discrimination and Disability Act which provides safeguards for you and many others with learning and physical disabilities.