Hi Sandra, in answer to your questions:
1) JobRoller does not currently include a built in import function, and although you may be able to find an XML plugin to do some of the importing, you may also need some knowledge of mysql admin in order to make sure fields are migrated into the correct location.
2) You can certainly add tags to listings if you wish, and these can be set up in the JobRoller admin as seen here on the
JobRoller admin demo. Search will include listing information and tags.
3) Yes, you can manually register users from the WordPress admin
4) Users can subscribe to a specific category feed if they wish to be notified of new posts in that category. Thanks.