OK, so I discovered that I can use an en dash (on a Mac, option-hyphen) instead of a plain hyphen to LOOK LIKE a minus sign, and FMP won't treat it as a list divider.

Problem #2 is still live, tho. I still can't figure out why I get no drop-down list or pop-up menu when I tab into the "Operator" field. Its contents are:
+
–
*
x
/
÷
**
^
so no numbers or letters (except for that lower-case "x"). Could that somehow be suppressing the display?