Depends on your Uni, but you'd have an advantage if you take the test.
Just take it, it's really easy.
not really, i don't think you should have to take the test as long as you have a C in english GCSE (or B in some universities' cases.
About the IELTS, I personally hate doing the Critical Thinking stuff... and if you're reading is not very fast, you are kindda disadvantaged. I know some adults who are trying to take it and they've failed on multiple number of times... it might be different for you, but i don't particularly like the test. Plus, it is quite expensive; don't waste your money unless you are sure you will do well.
it's not that tough really, but you have to check the unis requirement, as some would require it. not sure with this, check it thoroughly though .