You may be right about Queen's Indian vs. Catalan. My point was that black doesn't have to give white Catalan lines. The pawns at d4 and c4 with the fianchettoed king's bishop has classical and hypermodern features. Still, I do not think it's easy to learn and wouldn't recommend it to anyone who wasn't already accustomed to the English, Queen's Gambit, or Reti systems. For a player that had been playing 1.e4, they are all of the exact opposite ideas.
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There is no "Queen's Indian against the Catalan". In the Catalan there's a black pawn on d5 and in the QI there isn't.
The move order 1.d4 Nf6 2.c4 e6 3.g3 should certainly not scare Nimzo/QI players, as they are not forced to go into a Catalan, but can go into a g3 Benoni with 3...c5. And have the extra option of playing 4.d5 b5, although the main lines are also perfectly fine.
I have reviewed the comments, and believe that almost everyone has missed the questions. Gundamv is asking 1) Is the Catalan a viable option to playing 1.e4? 2) Is the Catalan a good choice? Is it easy to learn, and what are some good resources? The answer is no- to all of the above!!!
First of all, if you've been playing 1.e4, you know what to expect: Open king pawn game, French, Sicilian, Caro-Khan, Alekhine, all of which white has nothing to fear and has historical advantages in all, so just play, learn, and improve. Secondly, to even get the Catalan after either 1.d4, 1.c4, or 1.Nf3, black must play into it, so to speak. Black can play early c5s, f5s, Nf6s, and b6s at any time and you just won't get the Catalan. Usually, white can get Catalan lines against the Queen's Indian (1.d4,Nf6 2.c4,e6 3.Nf3,b6 4.g3,Bb7 5.Bg2... and black is even. Or against the King's Indian (1.d4,Nf6 2.c4,g6 3.Nc3,Bg7 4.e4,d6 5.Nf3,0-0 6.Bg2,e5, ect..and white's playing the King's Indian, granted, the fianchetto for white has historically strong results, but I'd take black's situation, but not unequivocally. Neither example is really a Catalan, really; so not only is it hard to learn, it's difficult to even get!
In my 20 plus years of competitive chess, I've only played the Catalan as white a handful of times (as a transposition from the closed Reti:1.Nf3,d5 2.c4,e6 3.g3 Nf6 4.d4.., ect.) with mixed results. and have never played against it once, because I know how to transpose 1.d4 players away from their favorite lines.
To answer the final question, first of all I do not recommend the Catalan. My recommendation would be to stick with 1.e4 and just keep improving, but if you really want to change, use 1.Nf3 with a view toward the Reti system of attacks (Reti, Nimzo Larsen, Reversed Sicilan, Reversed Grunfeld- no Catalan, no English).
Bobby Fischer, arguably the greatest chess player, played 1.e4 exclusively; while Karpov, arguably at least top 3, played 1.e4 rarely, and Garry Kasparov (top people's choice as best ever) and Magnus Carlsen (the present champion and still improving) play everything. But you're not them and neither am I. All I'm saying is that changing your opening approach, if you're below 1700 is not worth it. Take it from someone who did it, I was better off where I was!