I don’t think leaving the pieces in a separate pack is a good idea, like how would you even market that to get peoples attention? I would do 3 animals and 75-100 pieces for 5 bucks.
Example:
Tranquility Pack
Discover spring in a different light by exploring nature as it is and as it should be. Watch the blossoms grow and see the colours brighten with the
Planet Zoo: Tranquility Pack!
Take a walk through the meadows and fields of spring and discover 3 new species; the adorable
European Hare, the majestic
Mallard, and the powerfully prancing
Blackbuck!
Alongside this pack, you will have access to over
80+ new spring themed pieces including a variety of new flowers, vines, trees as well as a few new construction pieces like new wooden turbines, walls and more!