did anyone gave exam 4 recently. I don't have experience in risk management and reading case studies and ethics alone will help to pass or do I need to read all the exam 1 II III then sit for exam 4.

Each exam is (mostly) independent from the others. So you can take Exam 4 without reading Exam 1, 2 or 3. Exam 4 is also the easiest and with the least material to read so passing it will give you some confidence for the other exams.
Good luck!

I followed the same trend giving exam 4 first, then 3, then 1, then 2. However, if I could change that order, I would. You will surely pass exam 4, however once you pass, your 2 years time limit to pass the other 3 starts and exam 1 & exam 3 needs at least a month or two to prepare (maybe more). I would start with one of them, and if you pass it, you will surely meet the 2 year deadline. With the new 2019 syllabus, all might change though

Can someone confirm whether questions in exam 4 are entirely based on the case studies or will there also be questions on governance, best practices and ethics please?

The questions cover the case studies, the best practice, conduct and ethics, bylaws, etc.