fire, water, and grass type is important in this elite four challenge it seems. with WiFi, everyone will be willing to trade all the starters, so if you manage to do this, you will do well in the elite four. you really need a fighting type as well, and the monkey starter will help for this.
the elite four member that'll be a challenge is a the psychic. i suggest the penguin evo and a strong normal type would be helpful, but for the psychic/steel, you have the monkey.
for the champion, an electric with good sp defense and speed will be heplful vs half of the pokemon. the penguin evo may also come in handy here.