I want to see if I start reading them, but would like to know how many are they right now. Thanks
TL;DR: Just buy Disney stock. They will make money hand over foot.
I won't provide a full list of books here because first, it's fluid, and growing. Second, far better places on internet track them, such as:
This is - as the name suggested - ordered by in-universe chronological timeline; and marks books as Adult, Junior, and unpublished.
This should be unified with the future books list in the Timeline above, as they aren't always updated in sync.
In all honesty, I didn't actually find a comprehensive book list there, but it's the horse's mouth so should be consulted as a resource.
To answer "How Many?" question:
According to Wookieepedia timline, at this time (2015/12/19) there exists:
7 Adult books (of them, 1 game tie-in, and 5 are set before battle of Endor, so no direct tie-in to TFA)
This list doesn't yet contain official Alan Dean Foster novelization of The Force Awakens, which was released yesterday December 18, 2015 digitally but not in dead tree form till January.
17 Young Adult novels
3 of them are Junior novelizations of the Original Trilogy. Because Disney can always siphon more money from the kids so adult novelizations aren't enough.
There also exist too-numerous-to-bother-counting comics and short stories
Includes graphics novels.
Mostly includes things printed in magazines like Star Wars Insider etc...