A 120/128 is marginal.
Yes, you can make it work, but you'll spend a lot of time massaging the space on it.
The base install of Win 10 will be around 20GB. And then you run all the current and future updates.
An SSD needs 15-20% free space, so for a 128GB drive, you really only have 85GB space you can actually use.
And if you try to keep it "windows only" you're throwing away 1/2 the functionality of the SSD. You want your applications on it, to benefit from that same speed boost.
All those utilities and stuff.
Finally, the price v size ratio favors a 250GB over a 120GB.