A fresh install is the preferred method but many people successfully clone.
Your steam games will be fine left on the HDD either way. I dont know about GOG unfortunately.
Clone c: to the SSD. Make ssd the boot drive in the bios. boot up. make sure you have access to the hdd then change the drive letter assignments so that D; drive is actually D: drive again (the old windows partition will probably be assigned D: which moves the games partition to e:)
Run diskmgmt.msc when you are ready to change the drive letters. You might have to change D to F, then E to D and then F to, well, whatever you want. (just not c or d. LoL)
As always, please make a backup before you begin if you don't already have one.
Thanks! I plan on using the Restore USB to restore to the SSD once I get it rolling. Then I will put the 1 TB into a usb3 hard drive enclosure (still deciding which one-you don't want to skimp too much on enclosures-I had a cheap one back XP days that lost 2TB of data!), copy my Steam Games, and I should be set.
Like I said-nothing is as easy as it should be. I know formatting a drive over 2 TB takes some special software (I think Seagate has software that will let Windows 8.1 see the whole 3 TB)