Dear Mangai,
You have to follow the law. The law does not differentiate between short-term employment and permanent/long-term employment. The term "fixed term" is not correct as all employments are of a fixed-term nature, i.e., you employ an employee maximum until the age of retirement (sometimes you give extensions, but that is also fixed).
No law states that you have to give increments to your employees, whether of short-term nature or long-term nature. The law only specifies that you cannot pay less than the minimum wage. If you are giving increments to your permanent/long-term employees and not to your short-term employees who may be doing similar work, then you would violate the law (discrimination?).
Similarly, for leave encashment, the Factories Act provides for a minimum accumulation of 30 days and encashment. You have to follow the same in the case of both short-term employees and long-term employees.
Similarly, you can find out about other issues. The only difference between short-term employees and long-term employees is that short-term employees are engaged for jobs that will only last for some time. Otherwise, there is no difference.
KKT