You are on the right track, DX7 or just to confuse things how about a Futaba 7CHP FASST (I love my 7C). The radio link is almost bullet proof, but the DX7 is easier to find info on and has all those tempting E-Flite BNF models you can take advantage of fr fun. As to the heli,
the T-rex 600e will rock your socks, E helis always have lower vibes and are easier to setup, but have a higher initial cost. Nitro helis are cheaper to get going a bit but require tuning the engine, and buying fuel all the time. The 500 is very stable, but the 600 can lift more equipment so take your pick.