I use a 128 GB NVMe drive, which is sufficient for my Windows 7 OS, in fact I also put on a few games I access often.
Most of the games I run are on a 512 GB SSD Raid 0
Most of the movies / music / media I run off a 4 TB mechanical Hard drive.
I do not work on said computer and do not have much professional / CAD SW on it.
I would go with the 120 GB SSD for now as it can hold your OS and your IDE's / programming tools. Additional storage is not hard or expensive to add as long as you are not changing your boot drive. I got a new decent 4TB 7500 RPM HDisk few months ago for 75$ on sale. So keep an eye out, I see storage prices have been falling recently. Good luck