Hi, sounds like there is still a lot you are unsure about in IELTS. Always check my information page: http:///ielts-help-faq/ . Here are some answers to your questions:
1. Capital letters are not considered in listening or reading. That means you can use them, not use them, use them incorrectly, mix them up – nothing matters. Just ignore them. If you want to write all answers in capitals, do so.
2. In answer keys there are can sometimes be more than one possible answer. For example, “a pilot” or “pilot”. When this is the case, the answer key is written as “(a) pilot” which shows the “a” is optional. You can’t write like this in your test. You must choose one answer and write it.
3. You must write only one answer – singular or plural. This is a test, and it’s testing your understanding of plurals.
4. IELTS never write “one word only”. Are you using real IELTS tests which are published by IELTS. If you are downloading for free from other websites, you are not using real tests. Be aware of fakes. Use the IELTS Cambridge test books from 1 to 11.
5. BC do not write their tests. IDP do not write their test. The IELTS tests are written by a third party. Any difference between tests is random and not based on centers.
Sorry I don’t offer marking at present. See my main writing task 1 page: http:///ielts-writing-task-1-lessons-and-tips/
There are no hard and fast rules about organizing a comparison/contrast paper, of course. Just be sure that your reader can easily tell what’s going on! Be aware, too, of the placement of your different points. If you are writing a comparison/contrast in service of an argument, keep in mind that the last point you make is the one you are leaving your reader with. For example, if I am trying to argue that Amante is better than Pepper’s, I should end with a contrast that leaves Amante sounding good, rather than with a point of comparison that I have to admit makes Pepper’s look better. If you’ve decided that the differences between the items you’re comparing/contrasting are most important, you’ll want to end with the differences—and vice versa, if the similarities seem most important to you.