Hi Chrisitne Sung
You also need to complete boxes 1-7 on the SA108. You dont need to provide any proof at this time.
2. yes you show this as foreign income for the UK part of the year
3. yes you need to complete SA109 to show split year.
Please note though, a paper return is now classed as late and you will need to file online using 3rd party software to avoid any penalties -
Self Assessment commercial software suppliers
Thank you