Hi Korvax,
It really depends on what programs you plan to install and use on the new rig. In addition to the OS in the Windows folder, you will be installing your programs in the Program Files or Program Files (86) on the SSD for rapid access. Also on the SSD goes the MS Reserved Partition and an additional partition if you are considering Intel's Rapid Start technology, some SSD's small 10% partition for Trimming, etc. Your Libraries, App Data, and Data, BackUp Images and Intremental BackUp data, of course can go on the secondary HDD.
Personally I would buy a 256GB SSD which will hold everything you need for an efficient fast system (now more reasonably priced) and not have to worry about size limitation.
As to model, you will get as many recommendations as there are makers. Everything considered, including the software apps and firmware update package, and stability, I prefer the Samsung 830 or 840. Maximum PC's May Magazine reviewed SSD's and recommended the Samsung 840 Pro. It is faster, however more expensive and to date less time tested since it is new.
Recommendations are personal and biased by what all of us have used, but also backed by experience we've had with Win-7 and Win-8 builds.