I just purchased my first (ever) keyboard (Roland A-500s) with the SONAR X1 LE software. This whole midi/keyboard/controller world is extremely foreign to me... I am overwhelmed! I am trying to set up the keyboard to be played like a piano (I don't know if this makes any difference). But when I press on the bottom edge of a key on the keyboard, the velocity works well (sounds good for a light or hard touch). But when I press on the top edge of the key, I have to press really hard to get the sound. This is important when I play a black key with my first or fifth fingers, while playing any key with my middle three fingers. How can I get the velocity to work/sound the same for both the top and bottom edges of the keys?

katinka, I saw this post lingering, but you pose a legitimate question.
I'm not a piano player, but I have had some minimal experience with pianos. I am guessing by "the top edge", you mean closer to the pivot point? If so, then yes, it takes considerably more force to get the same swing from the keys. This, of course, has a dramatic effect on how velocity might be interpreted.
The A-500 has a synth action keyboard, as opposed to weighted keys. While the synth action is suitable for triggering synths, many piano/keyboard players seem put off by it, because it does not feel like a piano.
Understandably so.
For my purposes, I use the controller to trigger mostly non-piano instruments. To this end, it is very well  suited, and I find weighted keys somewhat distracting when playing non-piano instruments. However, I can fully understand how you would want it to feel like a piano.
From where I sit, you have two choices.
Adapt to the synth action keys, or consider a different controller.
I fully understand the importance of feel in an instrument, which your controller is.
I hope that is helpful in some way.