1. I regret to say you must be visa free for a period of one year before you can apply for citizenship. Accordingly, if you only got ILR in April 2016, you will need to wait until April 2017 before you can apply for citizenship. Secondly, if your GCSE grade was in the English language, then this is acceptable for obtaining citizenship.
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3. That was the situation up until July 2012. Up 'til then you only needed to be three years in the UK as the spouse of a British citizen in order to gain citizenship. However, the law was changed then, equating the position of people married to a British spouse with the general situation where they only gain citizenship after five years continuous residence plus one year visa free on ILR.
4. I know. It is confusing. However, if you look closely you will see it states that you have lived in the UK "for at least" the three years before you made the application. The situation is that you now need five years residency to qualify based on marriage. This website does not state that explicitly. However, that is the situation, i regret to say. You can waste an application fee finding out if you wish.