How many lessons will i need? - This will depend very much on previous experience, whether or not you'll be having private practice and how well the necessary information is absorbed. The important thing is to make the most of each lesson productively to get to the required standard as soon as possible.
Is it best to have private practice between lessons? - Yes very much so. You'll be able to practice anything done on lessons and gain valuable experience. The important thing will be being disciplined enough to still drive correctly and safely to not fall into any bad habits!