In Unova, I spent days just leveling up my Pokemon. It does no good just to rush unprepared into battles. (It took me almost two months preparing for the Elite Four!) I also used some Rare Candies, which are rare, so use them sparingly. My way to strengthen my Pokemon is to get them all up a certain amount of levels one at a time. Say I have 3 pokemon. I would level up Pokemon #1 by 5 levels. Then I would level up #2 by 5 levels. THEN I would level up #3 by 5 levels. If they're all even, I have a better chance.
Unava's population is 19,000.
003# Would be Serperior. But counting Victini from the beginning, then it would be Servine.
You have to have beaten the elite four and N, and to have access to the easton part of the unava region.
Be aware
Easiest way to find stronger Pokemon have a decently strong Pokemon first in your party use repel stay in a area and maybe a Pokemon stronger than you will show up.
They don't get sronger, but your Pokemon will get stronger if you battle them a lot.
arceus
Train your Pokemon and level them up by battling.
yes they are
The strongest (most powerful) Pokemon is of course rayquaza.
yes because arceus can be any type of pokemon
brick break