I took A-Level RS with OCR, I absolutely loved it.
Don't worry about the essay writing, your teachers will go through how to structure the essays, they're fairly simple anyway.
I didn't study the Islam unit, I done Ethics and Philosophy of Religion. Ethics is really interesting as was POR.
Even if you don't wish to study RS or Philosophy at University I found that it helped my essay writing skills as well as my debating skills and many others. I strongly recommend studying it if it is something you're interested in