The concept of the game is not mine - my publisher wanted this type of game.
I'm just in the process of getting on Steam and I will share my experience with pleasure.

I didn't have to go through a Greenlight process - this is only for indie developers, but if your game will be accepted by the community (screen-shots, description, videos and 100$ for Greenlight account) then you will get your AppID number. You must enter the number to "steam_appid.txt" and copy this file to your game folder. "steam_appid.txt" is necessary to initialize your Steam wrapper (steam_api.dll from SteamworksSDK; function SteamAPI_Init(): Boolean cdecl; external 'steam_api.dll'; procedure SteamAPI_Shutdown(); stdcall external 'steam_api.dll' name 'SteamAPI_Shutdown' ; ). After wrapping your game with steam_api.dll you must use SteamPipe to upload you game. This is a major part what I know for now. I will share my examples later.