Do Tax Credits count as income, and other question

Hi

I am a potential first time buyer and, although I won't be in a position to get a mortgage for a while, I have a few questions.

Do Tax Credits count as income for mortgage purposes?

As a freelance writer and editor, I am self-employed. At the moment I do my own accounts as they are very easy and I submit my own self-assessment. I have no need for an accountant. But do I need accountant-certified accounts to get a mortgage? And can I get an accountant to prepare certified accounts for past years? So, say in another year I'll have a deposit, can I get an accountant to prepare accounts for the full three years just gone?

Finally, I use my credit card as a debit card; I put all my monthly purchases on it, like food, groceries, clothes, petrol etc, as I get airmiles on it. I then pay it off in full monthly. Would this count against me when they ask about credit liabilities? Or is it only if you actually have a balance that you pay interest on?

Thanks in advance :A