Your questions are very specific, and would be hard to get solid numbers on.
For example, here is an article regarding engineering/science graduates:
http://news.medill.northwestern.edu/washington/news.aspx?id=94961
The number of students that graduated with a specific degree doesn't appear to be easily found, as the universities/colleges most likely don't need to report to a higher authority when they give out degrees, but you can find articles, again check professional societies, that will aggregate degrees by type to give some numbers.
To get the number practicing a certain profession will be difficult, but to get a rough idea you could check with the professional societies that deal with that profession and they may have an idea, as people will often work outside of their degree, unless they are required to have a license, then you could ask the state about numbers that are licensed (still just an estimate).
For the number of small businesses, you may check with the SBA, but the best bet would be to ask the states, as these should be registered, and they may be able to tell you the number by segment, though I doubt it will be free.
You may need to pay to get this information aggregated already by some marketing businesses, but, I am not into marketing, so I am not certain to whom you would want to ask about that.
