1/ Getting ready for the exams in April is too late. - I couldn't agree more. Two months are not enough to learn a subject properly.
2 Learning long English texts by heart is useless. - I don't really agree. The more you learn, the more you remember. The more you remember, the more you know.
3 Revising basic grammar material will not help you speak better. - On the contrary, your knowledge in grammar will help you avoid mistakes while speaking.
4 Looking up all unfamiliar words in the dictionary when you read books in English will help enlarge your vocabulary. - Yes, that's absolutely right. It is one of the best ways to enrich your vocabulary.