You are allowed. However, in most cases, it will be referred back to you local leaders for resolution.
You absolutely can. They receive personal letters all the time. However, I do not recommend sending questions directly to them, because they are so busy most questions are referred back to your local leaders. They used to take personal questions but the time to answer and the redundancy of the questions prompted them to request that we ask local leaders first. The proper channels if you have questions are first to ask the bishop or stake presidency, if they don't know they answer they then refer you to the area authority (Seventy), and if they don't know the answer it will be directed to the first presidency.
You're encouraged to contact a local leader of the Church (stake president or bishop) about your question before reaching out to the First Presidency.
Sure.
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