If this is classesd as self employment income then this will be entered on the SA103 with the SA106 only being compeleted if tax has already been deducted and you are looking to claim foreign tax credit relief.
Relief for foreign tax paid (Self Assessment helpsheet HS263)
If this is employment income then this will be entered on the SA102, again with the SA106 only being completed if tax has been deducted at source.
The SA109 only gets completed if you are claiming the remittance basis, which is a personal choice if you meet the qualifying conditions.
Further guidance can be found here:
If the income is self emplyoed, then national insurance will be automatically calculated.
If this is employment you will need to speak to the National Insurance office for further information on how to pay if not run through a Uk payroll. A DPNI scheme is also optional but further guidance can be found here :