How hard is leveling to 100? Are wild pokemons max 50 level? Is there an xp debuff for farming lower level wild pokemons? How is pvp, is there anything you gain from pvp is there a prize?

It's easier to level 1st evolutions without evolving than leveling evolved mons. Some wild pokes level differs e.g dragon's den/cerulean cave are level 40+. You gain 1 pvp coin per win which can buy items and exclusive PVP mounts/clothing, can also be rewarded end of the season if you're in ladder.

Is in PvP all pokemon becoming 50 level? Is leveling to 100 nearly imposible?

Uhh, should be full team of level 100 for PVP, and just level to 90+ without evolving then evolve and use rare candys if you want, so it's possible. Goodluck.