New Game Settings

Maincharacter

You can choose one out of four Main Characters, their elemental affinity, dating interests and your saved loadouts.

Difficulty

You can change the game length and difficulty modifier here.

If you want to unlock Achievements and new gallery entries, which are basically new start options, your difficulty modifier must be 100%+.

Traits/Profession

You can choose your Main Characters profession, traits and genes here.

Starters

You can choose your starters species, genes and traits.

Initially you can only pick from Base Species.
After you unlock a Hybrid Species in the gallery you can also pick them.

You will receive starting Essence based on what primary species you've picked for your starters. If you choose hybrid species make sure that you've chosen the right primary species, as Centaur/Mermaid and Mermaid/Centaur starters will have different essence.

Additionally you can see your starters species description, base stats and possible, as well as guaranteed skills.

Challenge Rank

You can unlock new challenge ranks by winning the game on previous challenge rank. They increase difficulty.

New Game+

You can only start NG+ by starting a new run and winning the game. It allows you to carry over 5 characters and equipped items. It will also increase the difficulty.

For more information look here.