I love the Samsung 840 Pro/850 Pro SSD drives - IMO - they are the best out there. A bit more budget conscious is the 840 EVO drives. 128GB/256GB are about the sweet spot - depending upon how many programs you need to install on the SSD. I have the 840 EVO - and have Windows 8.1, Microsoft Visual Studio 2013, Microsoft Office and Adobe CS6 Master Collection installed on it....and still have room to spare.
You might also want to consider a backup drive - I would suggest going with a drive large enough to image the SSD and backup all files on the HDD - so maybe a 3TB or 4TB drive - don't worry about speed as much on the backup drive - it is only keeping a backup copy....
I use SyncBack Free to backup my data - it works great and you can't beat the price....
It is a nice build.....starting to get the upgrade itch again.....LOL