Yes, there is a relaxation of marks.
SC/ST candidates: There is a quota system for Scheduled Castes, Scheduled Tribes, OBCs as well as for Physically Handicapped Classes for XAT 2019. There is a 5 percent relaxation in the marks eligibility for reserved candidates XAT 2019. For XAT 2019 examination, there is no specific allocation of seats in terms of numbers for the reserved categories of candidates.
Click Here to read more about the eligibility of XAT 2018.
Yes, it is good to do so. Many companies recruit candidates with working experience.
Yes, these are all tentative dates so you can expect other dates as well.