1. 2.7.x (later 2.8.x)
2. Problem, I don't own Delphi, and I don't think I could afford it right now. Also, considering the price and how often new versions come, I don't think I'd want to.
3. The same code base could support 3 and 4, as well as GLES. There are differences, but with a bit of abstraction it should be possible to support everything.
4. Supporting GLES 2 would be benefitial due to the many devices that support it.