Yes and that is based on working in Thailand which you are not allowed to do for a week as your Work Permit is expired, you need to organize quickly a new work permit or cancel this stay based on working.
That is the same, you can apply for the Extension of Stay based on unable to travel but have a plan B ready to go abroad, apply for a new Non Immigrant O visa and later the Extension of Stay.
If you are on an Extension of Stay, be aware that now the Work Permit is expired you need to cancel this Extension of Stay because you are not longer working in Thailand.
NO, you can only work for the company mentioned in the work permit and in the areas mentioned in de description of labor.
NO, with a expired work permit you are not allowed to work and have to apply for a new year but depending on leniency of the Ministry Of Labor where this work permit is issued.