Finding Seeds

Highest quality seeds are mostly found around Pleasant Rest Graveyard, towards the Goth household, and more towards the town (On the opposite side of the graveyard). 

Seeds are placed all around Sunset Valley. Here are some locations: 

Outside of Pleasant rest Graveyard, cliff lining the ocean water (In between house lots), behind the market, movie theater and bookstore, Central Park, science facility, behind most homes in Sunset Valley, and more! Most lucrative seeds are found in places that are hidden.

Omni Plant

The Omni Plant can be fed anything -- Fruits, veggies, fish, even books! Every time you feed it, the plant will duplicate the amount you fed it. It is not a specified plant like the Death Flower, it grows and duplicates what ever you feed it.

Life Fruit

Life fruit extends you lifespan -- That is all.

Death Flower

By eating the Death Flower, it buys you time from the Grim Reaper, like Life Fruit. If you have eaten the Death Flower, and should your Sim be on the verge of death, the Grim Reaper will not take you. *If you have the "Unlucky" trait, and you die, the Grim Reaper will not take you, thinking that it was a part of your "luck".

If there are any more questions, please comment below.