You will be lucky if you pay anything in the first year - two years with tax all depending on your income though

They will get you signed up to instantly pay national insurance via direct debit or send you a invoice but it aint much, if you think you will earn less than £4500 in the first year you can apply to opt-out from N-I contributions !!!, I personally am employed aswell as self employed doing car valeting and opted out from secondry NI contributions and it was accepted , you just dont know what you wil earn in your first year so they cant really argue with you but then again they get bloody plenty from me in my employment contributions anyways