I am not sure that writing a web app is the best way to learn common lisp; it introduces a lot of extra complexity (libraries, web server, etc) in a language that is itself quite complex. You'd better start from a simple CLI application as your first project.

Books: there is also Graham's "ANSI Common Lisp", which has a different approach from PCL; I found it clearer as first text (but PCL is a necessary reading anyway, for various reasons). But it's a matter of cognitive styles, start from the one that you prefer.

Absolutely download the Common Lisp Hyperspec and familiarize with it. Is the main everyday referemce tool of any CLisper.

Environment: Emacs + SLIME is the most popular option. Commercial lisps (and their free evaluation versions) also have good IDEs.

Have fun!