Case-sensitivity

Are we to assume that B == b, or are they different.

This tells me he does make the distinction, so yes, i'd say they're different. ;)

Am I right in saying that the only possible characters in the maze are:

A-Z
0-9
b
*

Is this right or can there be any lower case letters?

No, it can't have 0-9, the only characters are A-Z, * and lowercase b. 0-9 is only used in the file format. and no other lowercase letters except "b" (which is special)

You are telling me that doesn't contain 0-9

no. what i am telling you is that the maze doesn't recognize the characters 0-9.. those 0-9's are only used for saying "1 of T", "1 of b", "5 of T" and so on. once parsed, those numbers can easily disappear (depending on how you choose to store it in your script).