Hi there, in answer to your questions:
1) Currently we are working on making our themes responsive and more mobile friendly, however this is not a specific feature at this time.
2) Yes, you can create job packs which will allow you to determine the duration in which the job listings will run for. You can see the settings for this in the
JobRoller admin demo.
3) No it is not a requirement, you can remove this if you wish with some minor code modification. Thanks.