I bet XD
1. You get Lucky Eggs at certain levels or buy them at the shop. When you use them, you get double xp for everything(evolving, pokestops, etc.) You'll just go to your items pack and click on an egg to activate it. It makes it a lot easier to level up
. Here's a link to rewards by level:
All of Pokémon Go's level up rewards and unlockables in one list (update) | Polygon
2. You get stardust by simply catching pokemon, hatching eggs, etc, as well as if you successfully defend a gym. If you manage to leave a Pokemon at a gym, click the shop icon and you will have a reward I think in the top right of your screen.
3. *High 5* for Mystic XD You made the right choice