I am not entirely sure what the rulings will be on these fossils when they come out but I have a feeling that you cannot evolve the Omanyte DP4 from a Mysterious Fossil since it states that it evolves from a Helix Fossil. This however will not stop you from evolving the Mysterious Fossil into Omastar DP4 using a Rare candy because there is an Omanyte that evolves from Mysterious fossil in the current format. Please tell me if I am wrong and they are playing it differently in Japan.
As for a suggestion for your deck I am thinking Phione. It can help you get the evolutions that you need out of your deck, so that you can get Ampharos and Kabutops in play earlier, once it is knocked out you can use scramble energy, you will use fewer trainers/supporters which will protect yourself from your own deck, and if someone tries to de-evolve your pokemon to get rid of the bodies it won't do them much good because you have the whole line in play. I think that I would take out any combination of the POV, Copycat, or Celio's to make room for Phione since you won't need them that much, IMO.