I usually keep the form reader and displayer in the same cgi file if the form is redisplayed when it gets input so it can collect more input basically in a loop. A lot of the code is common like collecting user credentials etc. Of course if you collect and categorize these credentials a lot then maybe you really want to make up a module you can call for this to make all of your scripts smaller...

But see here for a discussion of large CGI scripts.

Custom modules for a similar kind of thing are most recently discussed here

You can nest if blocks into other if-elsif-else block and the {}'s which are required in Perl keep it obvious which block goes with which condition. Do try to keep it as straight forward as possible for your own sanity later though.

Update: Found info on how to link nodes and implemented it.