Picking up the Queens gambit declined?

I have been playing the Kings Indian Defence for the past 10 years exclusevly against 1.d4. Note that i am only 17 years old. Its been reccomended that i pick up the Queens gambit declined line since i have reverted back to 1.e4 and 1...e5 in response to 1.e4 to better my chess education by first learning the basic pawn structures. Im the kind of person when he plays an opening he needs to know his lines and research them. It will be very hard for me to pick up the QGD because its not like KID which is a universal set up. I will have to find a new line against the colle, london, and stonewalls which i literally know NOTHING about. I honestly only know the QGD from the white side so i dont really understand the plans or anything. I only know ONE single line literally which goes something like this 

Get "Declining the Queen's Gambit" (Everyman) and the GM Repertoire book on 1.d4 w/o c4 (GM Repertoire 11) by Quality Chess.

Both books were written fairly recently.  I think the first was written in 2011 and the second in 2012.

I'm not sure he should buy such books...they seem too advanced and probably don't exactly explain things "the easy way". Why not give something like Starting Out: The Queen's Gambit Declined a try? There's probably also some information that you can gather online. And i'm pretty sure that you can play the queen's gambit declined setup universally as well(i'm not saying it is a good choice though, it doesn't seem to make a lot of sense to block the c8 bishop without necessity).

I prefer Nge2 rather than Nf3. In the Nf3-line most players go for the miniority attack on the queenside with moves such as castling short, rab1, b4, b5 etc. With Nge2 white intends to play f3 followed by e4.