256 gb is minimum. It will be enough for both OS and office, but you may have only 1/2 ssd capacity left for data.  also when Windows save restore points and update it may swell.  512 gb is a more comfortable size.
I'm ordering a new Inspiron desktop, I have a choice of 256 ssd or 512 ssd. I need to know how much space Windows 10 Home and MS Office Home and Student edition will take up on the new ssd. If those two items don't take up more than 100-125 GB the 256 might be large enough. How much space is left on a 256 drive after formatting? Thanks!
Size of Windows 10 Home and Microsoft Office