Affiliate Marketing Secrets

I am planning to start a GPT website, a site where members complete offers from my affiliates, i get paid and i give 50% back to the members in the form of points which can be redeemed for vouchers such as amazon vouchers, xbox points, paypal etc.
CPALEAD, the company providing the affiliates pays via paypal in sums of $50
I am from the UK and the american form i require would be the W9 but i cant seem to find the UK equivalent.
I am only 18 though I have good GPT knowledge and experience so ANY knowledge on how i would need to pay tax etc would be much appreciated.