maxed out stats on all pokemon?

No I don't think so

No...the action replay is the only way to do it...giving a Pokemon boosts such as Calcium will only raise it so much and there is a limit of how much you can feed them.

I don't think there is unless you battle with them heaps...

I think you can only get max stats is by a Pokemon team or a long code

You can EV Train your pokemon. >_> Cheating isn't always the answers to things.

If you want some high stats, you should battle Pokemon with good EV's. That way, when your Pokemon gains a level, their stat should go up by 5 or 6 in the stat that the wild Pokemon had high EV's in. For example: Battling an Alakazam, who has 3 Special Attack EV's, which is very good. You constantly battle Alakazams until you gain a level. You'll notice that your Pokemon gained 5 or 6 Special Attack points.

That's just one example. Some Pokemon have 1 or 2 EV's, and some have it in two or three stats. I could go on. But if you EV Train your Pokemon against other Pokemon with good EV's, you should gain some good stats.