128GB SSD is "just enough" for Windows and a few programs. Install most programs on the HDD if you can, the difference in loading programs will be not too significant. Most people can wait an extra second or two for a program to load.
You have to be sure to set all apps that do downloads to save the downloads to the HDD, not the SSD. Downloads are very slow compared to disks, even HDD, so saving downloads to the HDD makes a lot of sense. You can move things around later if you wish...
I usually recommend a 256GB SSD for Windows, since Windows itself will eat up disk space with every update. This is because Windows keeps all old files replaced by updates in hidden compressed folders. With enough updates, your disk will fill up eventually... 128GB will do ok as long as you manage the downloads and storage of large files onto the HDD.