>>4
It's a huge language. It's easy to be productive when you only know a subset of it. If you know scheme and the equivalent sort of code in lisp you are in good shape. Some things to add on would be macros, clos, the standard library, and how the community package system works (I hate it). Then there's things like loop, which I can never remember, and other features that I never use, like conditions.
>>5 is good. It will take you on the tour and you can pick and choose what you want.