Q on one off non paye income recieved

Hi. I did contract work in middle of last year in between employments - i.e. after redundancy in early 2018 and a new employment after the summer 2018 - gross earnings 25k. I am a PAYE worker in 2019 and have no plans to do contract work in future. My questions are:
1) As I have to fill out form 11 (as tax will be greater than 5K), do I need to register for self assessment and get a ROS account?
2) As I have no non paye income in 2019, can i de-register for self assessment after as I do not wish to be doing this going forward?
3) When paying the balance of tax due for 2018 in November, what do I do about the preliminary tax element for 2019? My taxes for 2019 are all up to date as its paye income?
Thanks.

In response to your questions:
1) yes, and you'll need to file electronically;
2) Yes, you can de-register from 31 December 2018. You can do this through your ROS account;
3) Assuming that all of your income is PAYE and tax is correctly deducted then you won't need to make a preliminary tax (PT) payment. In 2019 you can base your PT payment on 100% of your prior year liability (calculated as per the Form 11) or 90% of your current year (2019) liability. As you won't have any non-PAYE income for 2019 you should have no PT to pay on 31/10/2019.

Thats great. Thanks for that response. Must get ROS set up promto!
Can I deduct expenses such as business calls, office expenses for the work from home from this income like a normal business?