Most students bring food and I think the committees like it. Allow one hour. Someone is generally late and if the thesis was interesting, discussion usually lasts longer than 10 minutes. The background section should be very short and focus more on the methods and results. Discussion is generally short but question and answer generally addresses discussion type issues.
Students can invite anyone they want.
Students rather than faculty generally decide whom to invite. This is a very different skill than presenting results in writing. Looking professional generally helps one feel professional and is good practice for future presentations. The defense should take about one hour. The presentation itself should last about 25-30 minutes, with the remainder of the hour devoted to questions.