I agree with Crumb.
Cubic IDE is the way to go, but it is still good to get the Developer CD 2.1 because it has the Amiga Rom Kernal Manuals in AmigaGuide format. They are OK for referencing, but if you can, you should try and at least get the actual Libraries RKM book. Although it is hard to find and the same content is on the CD, it is easier to work through the actual book. At least, that's what I found.
Good luck.