Is there a way I can allow a longer field label for a custom field? I want to include some simple instructions on what format the field entry should take and the field label would be the ideal place to do this.

The database itself has a limit of 50 characters for the field label, so you are restricted by that limit unless you change the field in the exp_weblog_fields table.  This is a good feature request though, so I would suggest you put in the Feature Requests forum.

Done..thanks Paul