What are you going to use the PC for? I am assuming Gaming.
You can use the i5 8400 without losing anything in performance.
Did you consider an AMD based System. (Better bang for buck) either a 2600X or 2700X.
Do you have a monitor?
Keyboard mouse?
Are you happy with the onboard Sound?
How will you connect to the internet (Wifi or cable)?
I would suggest a PCIe M2 ssd rather than the SATA SSD you currently have.