ideally, how far should the brake lever go?

I don't know. I think it might be the wrong question. I like to set my brakes up with about 3mm of clearance from the rim on ea. side. How close they are in relation to the rim generally determines how far the lever pull is. As far as I know, the length of the lever pull isn't adjustable in any other way.

Do you mean how far should the lever travel <i>before</i> the pads contact the rim or how far should the lever travel <i>after</I> the pads contact the rim?

after the pads contact the rim.

ideally, how far should the brake lever go?

Your brake levers should be adjusted so that the lever doesn't hit the bars when you are applying maximum force. Beyond that, it's personal preference. Some people like to have "instant response" and so they set their pads so that they nearly touch the rim. The primary down side to this is that you have to use the quick release to get the wheel out. I leave mine set so that a 23 mm tire clears the pads without the QR release. YMMV