Leave "To" blank for your current activity/occupation, or if you're not sure about leaving dates blank, you could put the (future) date that your current work authorization is due to expire.
I assume the yes/no question about a job offer is during the online questionnaire. You should answer 'no' to this question, because (a) your job offer is irrelevant - you can apply for an open permit regardless, and (b) you want the questionnaire to ask the sequence of questions that leads to the open work permit application.
I assume the yes/no question about a job offer is during the online questionnaire. You should answer 'no' to this question, because (a) your job offer is irrelevant - you can apply for an open permit regardless, and (b) you want the questionnaire to ask the sequence of questions that leads to the open work permit application.