Well firstly, what you want to do is infect another worthless Pokémon with it and toss it in the Box. That makes sure you have another 'backup' in case something goes wrong and your Pokémon lose the infection. Afterwards, depending on the areas available to you at this point in the game, you can use some online guides and this page
to make a plan. To answer the second question, yes you can; there's a group of Berries that reduce EVs (somewhere on this
page), and if you calculate who has gotten what so far, then you can reduce certain EV stats to zero.