Fallen Darkness mod (Need help)

I will need some people to help me with the coding and the programming for this mod. Keep in mind that this will be my first mod, and quite honestly? I have no idea what I'm doing. So some advice and ideas would be nice please. Also, would someone please tell me what I need to make this mod?
I do have some ideas on what I will be modding when I can.

{Mobs}
Thief- Follows you to your home, locates the door, and goes through you're chests.
-Spawns by itself
-Cannot go through locked doors
-Will run away if chased
-Drops the stuff it takes, also gold coins

Hawk- Flies around the sky, and sometimes lands.
-It will fly away if you get too close
-Drops feathers
-Spawns in groups 7

{Items and blocks}
Keys-
-Can be used to lock doors by right-clicking a wooden door

Marble-
-Spawns underground, or on the walls of caves
-Can be crafted into marble tiles for decoration

Cave slime-
-Spawns in some areas on the floors in deep caves
-You can mine with your hand to get slime balls
-You can place the slime balls on the floors to make it slippery.

This is just a rough idea of the mod I'm planing, but I will be adding more stuff later. Also, like I said before, some help would be really appreciated :)