There is not a set number. It is up to the discretion of the site.
Five.
If you visit the Math leaderboard via the Match category page, you will see many great answerers for this month and previous months.
there are about 250 gold contributors.
No, anyone is allowed to bid for new jobs. An electrician needs a journeyman's license to legally control and supervise one electrical construction project under supervision of a master electrician who can obtain the electrical building permit and who is allowed to supervise and control as many projects his capability will permit.
Because that word may offend some or many of the users of the community. Using inappropriate or harsh language is not allowed in the website. Use of dignified and decent language is expected from all contributors.
Anyone (including you) can answer (or edit) questions. This is a "wiki" site that is open to everyone. There are also experts and supervisors in each category who provide as many detailed answers as they can and also supervise the other answers for quality.
thousands.
There can actually be a multiple number of supervisors in one category, I've once seen 4 supervisors in one category! But it depends on how busy the category is, sometimes and usually the category may need more then just 1 supervisor for one category of interest. So there are usually a multiple number of supervisors, supervising a category. But usually less than 5, but hey, the more the merrier!
obviously if i can post this question and then answer it myself. There are many people who volunteer their time and are dedicated to making sure that the questions are provided with valid answers. Vandalism, spam, foul language, etc are not tolerated and the contributors perpetrating these things are dealt with accordingly. Many of the contributors go out of their way to make sure that the answers that not only they are providing, but also the answers that others are providing are accurate and many of the contributors spend a lot of time researching their answers. In addition, many of the Category Supervisors specialize in the categories they supervise in real life. That is to say that they are either an expert in that particular field or their hobbies in life revolve around that field. There are answers that are posted that are not correct and they don't always get caught immediately but they will be caught eventually. I suggest you look around the site and give it a second chance. If you look a little deeper you'll find that appearances at first may be deceiving but what really counts is on the inside.
many contributors right from Planck to Einstein, Bohr,etc. a proper answer has not been given yet by anyone.
Depending on the level and category, anywhere between 15 - 36. The levels dictate the rules on how many people will be allowed to compete at that division level.
Many, many thousands of people have contributed to our knowledge of chemistry.