I want to travel from Delhi to Manglore with the Nizzamuddin Eruklam Express (12284). Is food offered for free to sleeper section travellers, or do we have to pay for that?
When it reaches Manglore, is it usually on time or delayed by hours?
Yes, you will be offered food for free in the Nizzamuddin Eruklam Express (12284) as you are already charged in ticket.
For evidence see the screenshot below which I took in the IRCTC website while booking ticket for the same train.
To answer your second question the train usually reaches Manglore on time.