If you decide I pick up one of these openings (or both), you need to make sure that you remain flexible and don't go into "system" mode where you think you can just play certain moves no matter what your opponent does and expect an advantage.  For instance, don't play the English with the idea of playing 1.c4 2.Nc3 3.g3 4.Bg2 5.d3 6.Nf3 and 7.0-0 (in whatever order) in all your games.

I actually recommend the Catalan, but play it via a 1.d4 move order.  That means 1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.g3 and 1.d4 Nf6 2.c4 e6 3.g3.  You'll obviously still need something to play against the Queen's Gambit Accepted, the Slav, the King's Indian, the Grunfeld, the Benoni, The Benko, the Dutch...

My point is that if you want an opening advantage after 1.d4, you need to play 2.c4 (or 2.Nf3 & 3.c4) and be willing to play good moves against various Black setups.  This often means leaving the realms of the Catalan or English.  However, you can still get a Catalan against Queen's Gambit Declined, Queen's Indian, and Nimzo players.

It takes two to play these openings.

After 1.c4 the game might not be a proper english. 1...e5 and 1...c5 usually gives English positions although transpositions to other openings are still possible. After 1...Nf6 and even more often after 1...e6 and 1...c6 the game could either go to Reti or regular 1.d4 openings.

The Catalan can be seen a response to a queen's gambit set up using a fianchetto. (1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.g3) or as a way to play something else than the Nimzo or Queen's indian defence after 1.d4 Nf6 2.c4 e6 3.g3 (not 3.Nc3 Bb4 or 3.Nf3 b6) when d5 gives the Catalan. (Note that 3...c5 gives the Benoni or english). It is also commonly reached from the English, like 1.c4 Nf6 2.Nf3 e6 3.g3 d5 4.d4.

Usually, it is recommended that club players should first grasp the classical openings before choosing openings with more modern ideas. The english and even more so the Catalan are quite sophisticated openings which might be more difficult to understand than those after 1.e4.

Take a look at games by Ribli, Wojtkiewicz or Ulf Andersson. They play/played both the english and the Catalan. If you like the positions, why not try these openings yourself? 

What you could do is to start with the english following the repertoire by Kosten in "Dynamic English". If you decide that the Reti approace to 1...e6 is insufficient then you could try Catalan vs that. There's also a book coming out in a few months. "A strategic opening repertoire for white" by Hansen and Donaldson. This will recommend a repertoire using 1.Nf3 with the English and the Catalan as main choices.