I've thought of three other finite collections that might be possible -- gnomes, inventions, and objects upgraded by someone with the handiness skill.
Also, Turoskel brought up a point -- the things you get from dumpster diving don't register on the collections page. I'd add that neither do things dug up with the miner. And the game doesn't always give you credit for plasma bugs, fireflies, and mushrooms. (And would we consider mushrooms to be a separate collection or group them with plants?) So could we go with something along the lines of as long as you didn't buy it, it counts?
Oh, and I agree that 4 days is possible for the birth, but if you want to make it easier, you could say the founder has to "try for baby" by the end of Day 4.