Well, there are going to be lots of Shadow Pokemon since Cipher has had years to create them. Something I should let you all know is that both the Relic stone and the purification chamber have both been destroyed. But don't worry, I have what I think is a neat plot idea that will allow Shadow Pokemon to be purified and yes, it involves Celebi. xD

There will be random encounters with random Shadow Pokemon. But yes, teams will be pre-planned mostly. You can edit the teams though as events happen.