a 32GB drive will only be 29.8Gb of usable space due to.. well, the way binary and the manufacturers counting works. (I don't want to complicate this, just trust me on this one)
as an example the size of my "Windows" folder (Windows 8.1) on my C drive is 18.5GB, and I haven't even looked at my users folder and program files for basic software that you would need. Although it is technically possible to install Windows on 32GB, the free space will honestly start disappearing and before you know it those spare few GBs have turned into spare MBs, don't forget you'll want to save a few GB free for a memory dump, which will want as much storage as you have RAM.
Even if you have all software and user files on a separate hard drive the programs will still save temp files and the like to the C drive. The loading time you would save by getting an SSD would be spent by you de-cluttering the PC, so I'd recommend just waiting until you can afford a 64GB SSD and you wouldn't have to worry so much about running out of space.