How much information can be added to the "fill-out field" on survey answers? Is that space expandable? I have added multiple answers, but on some I want to allow comments. However the "comment box" is not an option following individual answers.

It is best to use the comments box for longer answers. The single line text box is very limited, although I do not know the exact number of characters allotted. I believe the comments box allows for 8000 characters.

Thanks, Scott. But is it possible to put a checklist of items in a survey and then add a comment box to the same question for people to insert their own ideas or suggestions? I guess the question is, can you mix the type of answers you request, including both radio buttons or check boxes plus a comment box?

No, you would need a different question, maybe something like "Additional Comments:" of type Comment Box.