Hello Ranjith,
regarding point 1 and 2) There exists a Job scheduling API (JSDoc: Namespace: jobs) for XSJS which you can use to schedule your jobs. You should NEVER update directly any system tables to activate a job.
Regarding point 3) There is the XS Job Dashboard were you can control the jobs on a single level, but not on a multiple level (e.g. marking several entries and unschedule them).
Best Regards,
Florian