Regarding LOC and APPR: On some aircraft (eg B737) you have to arm both LOC and G/S but on the airbus it assumes that you want to follow the localiser if you want to descend on the glideslope, therefore by pushing APPR you are arming both.
The way you were doing it isn't wrong, just more work! In fact generally I will press LOC only until I have definitely been cleared to descend on the glideslope as well. So if I am cleared for the approach I press APPR; if I am only cleared to intercept the localiser I press LOC (and then when ATC later clear me on the glide I press APPR).
Regarding localiser only approaches, yes, you have to initiate the descent. Like I said on your other post, we do that at 0.3DME before the descent point because of inertia. Again this is where the TRK/FPA button is a beauty. At 0.3DME before top of drop, we dial up -3.0 (3 degress down, or whatever the glidepath angle is) in the vertical speed window, pull the V/S knob and the aircraft will descend at 3 degrees. You can do it in V/S but this is much easier.
If you have approach plates to hand, there should be a box somewhere which shows height vs distance to be on the nominal glide. So compare your DME reading vs your height and make corrections to get yourself back on the glide. E.g. at 5DME you should be at 1500ft AGL, 4DME 1200ft etc