I generally echo YRAMagicMan here. I'd definitely pick up Expert Card Technique and Expert at the Card Table. For me, Card Control is less of an essential, but there are a few nice bits and pieces. My recommendation is to study ECT and EATCT at roughly the same time, not waiting to master all the techniques from one book before moving on to the other. The reason being that you won't ever get round to the second book if you're waiting to achieve perfection in the work from first.
Erdnase is an ever-unfolding enigma, susceptible of multiple interpretations, and can therefore be a lifetime's study. The Hugard and Braue book, on the other hand, while generally in the reach of the intermediate card handler, has some strange curiosities which will slow down your learning process. Check out the Zingone Perfect Table Pass and some of the centre deal ideas, for example.
Anyway, after you have a good grounding in RRTCM, ECT, and EATCT the world of card magic is your, to coin a cliche, oyster. There are loads of routes you could go from there, or, if you wanted to, you could make a decent reputation and career just with the material you'll already have.
