I've been researching all the Steam Greenlight data I can find, and I have some findings:
- It takes about 60,000 Yes votes to get Greenlit.*
- You will only get ~6,000 Yes votes organically from within Steam. The rest your must gather yourself. [source]
- The first 3 days are very important. In that time you'll be seen by the same number of Steam users as you will in the next 20 days. [source]
- Valve chooses game to Greenlight about every 2 weeks. [source]
- A Greenlit game can expect to make ~£109,000 over 6 months, selling ~20,000 units. [source]
* This is my educated guess based on reading many articles and comments on the subject. As the people with the current highest Yes votes get Greenlit, this number changes to suit the new highest voted left. There are also other factors.