1.
Hmm, couldnt understand the first question properly. But, evolving pokemons at the end (level close to 100) is bc of the experience that it needs to gain a level increases when the pokemon is evolved. Every pokemon has its own base experience values. When the base experience value is higher it means you need more exp to level a certain pokemon. (The amount of exp you need to level up a pokemon is proportional to the base experience value) For example, bulbasaur, ivysaur, and venusaur has an base experience value of 64, 141, 208, respectively. You can see that the base experience value doubles each evolution, which means if you evolve the pokemon it would be harder to level up the pokemon. (For more info about experience systems in PRO check out the link. https://prowiki.info/index.php?title=Experience_System)
2.
Yes, there is a way to reduce the Ev stats of a certain pokemon. It would be said if you can't reduce the Ev stats. There are Ev reductive berries inside the game. Since, there are 6 stats in pokemon games, there are 6 berries to reduce each stats. If the a certain pokemon consumes a berry the according Ev stat is reduced by 10.
Pomeg : Hp | Kelpsy : Atk | Qualot : Def | Hondew : Spatk | Grepa : Spdef | Tamato : Spd
You can obtain them from 3 different ways. First, collecting them from trees. Second, by winning the berry tower located in rt 13 Kanto, middle of vermillion and fushia, the reward are Ev reduction berries. Last is the berry shop. After beating the Pumpkin King boss in rt 6, you can access the berry shop located at goldenrod. (You can purchase each berries 3k/ea)
3.
Sadly there are no other ways to level up without increasing your Evs other than rc, to gain exp you have to kill other pokemons and if you do you'll gain Evs. If you dont want to consume berries, I recommend you to first Ev train your mons. Since, the max Evs you can give each pokemon is 510. (252 max in each stats) So, if you already give 510 Evs to your pokemon it won't gain additional Evs.
I hope this answered your questions well :3
GL playing PRO !!
I wish you have fun in further games !!