beginner el form

[Adam <nospam@example.com>]

At the top of the "Programming in Emacs Lisp", before and around the section
Practicing Evaluation, examples are given for the novice to evaluate by c-x
c-e.  And this does produce the result in the minibuffer or echo section
below. 

My question is, How should create a buffer in which the results will be
echoed in the buffer, like in a lisp-evaluation-mode ? 

In particular, what extension whould this file/buffer be called. Presumeably
name.el where expressions are evaluated by highlighted and evaluated by c-x
c-e  but then doesn't this required the major-mode to be changed every time
the file/buffer is opened ? 

I am looking for a file in which I can incrementally create an emacs-lisp
program, will much trial and error, where screes of text can be printed as
a result if necessary, and the minibuffer is just not big enough. 

Now, if some setup *---interactive-mode---* stuff could be included at the
top of that buffer, then that would be ideal. Perhaps it is an
"self-evaluating form" that I really need. 

Any suggestions or comments appreciate.