several newbie pokemon questions?

[Terry]

I'm playing generation III, emerald, to be specific. I have a handful of questions that I can't really figure out from the wikis.

1) I keep hearing about effort values (EVs). They're hidden somehow and separate from a pokemon's nature, right? how exactly do they work?

2) I hear there's a small bonus to various stats depending on what kind of pokemon is being battled as you level up. Is there a list of what stat bonuses each pokemon give? more importantly does this "bonus" only kick in based on the pokemon you defeated RIGHT AS you level up, or does every single battle count toward that bonus type?

3) Higher evolved pokemon (e.g. raichu vs. pikachu) have higher base stats. That means the longer I wait to evolve a pokemon, the lower his overall stats will be, right?
3a) Can I just make that up by feeding him vitamins (carbos, calcium, etc)? like, if I wanted to, could I give a pichu an everstone, get him to 100, then feed him enough vitamins to make him as effective as a lv100 raichu would have been?
3b) is there a cap on the stat gains you can give a pokemon through vitamins? like, after giving a pokemon 10 carbos or something, does it prevent you from giving them more? does that affect 3a?

4) pokemon that evolve via evolution stones, like lombre. Evolving them means they stop learning new moves, but let's say I evolve lombre into ludicolo, then level ludicolo to 49, which is when lombre would have learned hydro pump. Can I then take ludicolo to a move relearner and teach him hydro pump that way? or do you simply have to wait to evolve these types of pokemon until you have all the moves you want?

Sorry I know that's a lot. If you can even answer one of these questions please reply