1) Annual leave - The law lays down the minimum guidelines however there is no harm if an employer wishes to go ahead and extend the benefit beyond what is mentioned. It is absolutely ok to grant AL before the completion of 8 months, and it can be done on a pro rata basis.
2) If an employee who joined in Apr 2018 has finished his entire annual leave of 15 days, is he eligible for new annual leave in Apr 2019?
This totally depends on whether you account for leaves on a calendar year or FY basis. If you follow the FY basis, the new annual leave eligibility will start from Apr 2019 onwards.
3) Casual & Sick leave - Can we carry forward these 2 leaves to the new financial year?
The law says no; however as i said before there is no harm in giving more benefits to employees than what is mentioned in the act. If you carry them forward, it will increase the employer's liability; however if still you have to; i suggest you make a policy and convert un utilised leaves in Privileged Leaves and carry them forward.
4) Al encashment - Is it mandatory to pay the employee for the balance leave at the time of separation?
Yes, Please read sec 21.5 of the said act.
15th January 2019 From India, Delhi