If you want build the tablebox with a user-defined field-order you will need to store the selected values into a variable, something like:
varFieldOrder = '$(varFieldOrder)' & getfieldselections(YourFieldListbox, '|') & '|' &
then you could loop through these variable. But you will need some more logic to clear the variable after creating the tablebox and handle any errors. Easier could be to create such field-order by the tablebox in steps - first step: tablebox wille be created with the first field, second/third ... step will be to append field after field.
THe easiest way would be the user adjust the tablebox by drag 'n drop ...