Different editions of Symbian

Question

I have to built a project in Symbian. I am having and confusion and had some question related to Symbian version.

1. What is the difference between Symbian^3, S60 3rd edition and S60 5th edition?
2. Is there any major difference as coding point of view with Symbian^3, S60 3rd edition, S60 5th edition?
3. Does the code built in S60 3rd edition will work in S60 5th edition or code built in Sybmian^3 will work in S60 3rd edition, S60 5th edition or vice versa?
4. Which IDE do we have to use for Symbian^3, S60 3rd edition, S60 5th edition?
5. Which language does we have to use for coding in Symbian^3, S60 3rd edition, S60 5th edition?