A couple of months ago I set up a new website that's earning me about £200 / month through affiliate advertising.

I also have a full time job where my employer sorts out my tax through PAYE (this salary means I am in the high tax (40%) band)

I am trying to sort out the best way to pay the tax due on my website income.

1) If I do a self assessment, will I have to pay 40% tax on this income?
2) What happens about national insurance?
3) Does my employer still sort out my full time tax and I just do the extra through self assessment?
4) Would a be better off setting my self up as a sole trader or limited company?
5) As I maintain the website at home, does this mean I am using my house for business use (will this effect my house insurance / mortgage?)

The more I look into this, the more complicated it becomes, especially considering the small amount of money concerned!

Thanks in advance.