No, really.. It doesn't matter if you level up while EV training, you can't miss any EVs! It eases your job helluva lot if you EV train them via battling too
Well, let's say you give your pokemon one Protein. It gives your pokemon 10 EVs to attack. You can only use 10 proteins on one pokemon, but you can then continue giving 10 Calciums on the same pokemon etc
In other words, you can get 100 EVs to one stat using vitamins alone.
And pkrs will only come in handy if you battle pokemon to gain the EVs
For example, if you battle a Zubat that usually gives 1 SPD EV, you gain 2 SPD EVs if your pokemon has pkrs. Pkrs also double the EVs gained by using power items (eg. Power Bracer etc.)
Don't worry, you'll get the hang of these things soon!
IV breeding is very simple, you just pass down IVs basically