@NeoGuilt: You always, always, ALWAYS have to place an Active Pokemon before you check for any Benched Pokemon. And once you set that active Pokemon it can't be changed during set-up - even if you draw a Pokemon during the mulligan draw (you can bench it, but not place it active).
@Rappermi: Old Amber counts as a Fossil technically, but it can't be searched via Fossil Excavator since it doesn't have 'Fossil' in its name. And by extension, you can't use Fossil Excavator to search for any new Aerodactyl. (Old are fine, since they evolve from Mysterious Fossil.)
Fossils count as Trainers, so you can't use Roseanne's to scout for them. During set-up they are treated as Pokemon and you can play them down. However, starting with turn 1, they're treated as Trainers when outside of play, and Pokemon when inside of play. You can attach energies to them, evolve them, and whatever you wish when they are in play (except Retreat, by the card's text).