My 1st time to file Self assessment tax return and how much tax shall i pay in UK property ?

I am a non-resident landlord buying a student accommodation unit in Liverpool to rent out in Q4 2013. This residence was jointly owned by myself and my hubby. The unit was managed by PM Co. The PM company offered us the assured rent GBP 4000 a year. This is net amount receivable and we don't need to pay other fee / charges but actually PM Co. already charged 8% from rental income gross.

We have applied a Non-Resident Landlord scheme with no tax deduction and received the approval letter from HMRC this early year. However I just received another notification asking us to file the self-assessment tax return.

I surfed HMRC website and learned for a while. I got some questions.

Form SA100 - I think I am okay how to fill it;

Form SA105 - Under Section Property income

Box 20 "Total rents and other income from property", shall I just put the net rental income I received or I need to write the gross rental income (including this 8% mgt fee)

Box 21 "Tax taken off any income in box 20", what does it means ? I shall fill it?

Box 36 "10% wear and tear allowance", can I count and fill it ? (or i shall leave blank here as this is handled by my PM Co.)

Box 38 "Adjusted profit for the year" and 40 "Taxable profit for the year". if I simply received a net rental income from PM company, shall I just put GBP 2000 there ? (The rental income GBP4000 was divided by 2 to myself and my hubby)

So last question is if I earned GBP2000 rental a year, shall I pay tax ? and how much ? Thx