If you fail a paper you'll get the result just after the closing date for the next exams so you won't be able to resit immediately.
You don't
have to do another refresher course if you fail, its up to you to decide if you need it. If you fail any one subject more than 4 times or use up six attempts in total without passing everything you have to do a mandatory 60 hours of 'remedial training'.
You can go on to Module 2 with resits outstanding from Module 1. Whether you consider this is wise or not is another question.
4 attempts, see above.
In the UK, you must complete all papers within 18 months of your first attempt. You must get license issue within 3 years of your last pass. If you want an IR you must get the IR test passed within 3 years of your last pass at ATPL level.
You will not necessarily be told all this before you buy your course, although most training providers will do their best to do so. You are responsible for finding out how the licensing rules apply to your situation.
The LASORS are
here