I might wait on reading "Witcher 3" guides, at least until you confirm you are stuck/near more guidance while actually attempting to play (or can't get near your machine and need a fix).
Reading the source novels, or watching/playing the previous games will only add to understanding of what is going on while you initially immerse yourself into the world.
Not all the books exist in English in print format, but the missing ones are being brought out by Gollanz (starting with the second volume (Sword of Destiny) on the 19th May).
The correct reading order is:
The Last Wish (short stories).
The Sword of Destiny (short stories - currently fan translation only).
Blood of Elves
Time of Contempt
Baptism of Fire
Tower of the Swallow (fan translation)
Lady of the Lake (end of the canon saga, fan translation)
Also (currently in fan translation only) the sidequel/prequel Season of Storms.