an SSD in combination with a fast HDD for all the data can indeed boost the performance of your PC.
But not in any case. It doesn't make sense in combination with older hardware. For example an older CPU can be the bottle neck and an SSD wouldn't give you any advantage. If you can hear the HDD working hard very often, then an SSD may be useful. Or have a look at the Resource Monitor (via Task Manager, Performance tab), while using your PC. If the blue line stays at the top end of the diagram Disk very often, while the green indicated transfer volume stays in the single digit mega bytes and the CPU usage isn't very high, then an SSD could make sense.
Due to the technique used for the data management of SSD's, which includes a hidden reserve, it's reasonable not to use all the space available for the partition(s). Just let a few GB's unpartitioned. So you can increase the reserve available. An SSD with a high filling level will loose a greater part of its writing performance.
Your system partition contains 80 GB of data, so I recommend a disk size of at least 128 GB. You can use Acronis True Image for cloning your disk, or any other software of that kind. But it's important not to do a sector by sector image (as the Linux command dd will do), because that would copy empty disk space too. And the controller of the SSD will consider these blocks as used, resulting in a decrease of writing performance.
So the question is, what components is your PC made of?