Need two and one half day agenda for Positano

Positano is so small, you'll have plenty of time left over to see the other small villages nearby in 2.5 days. There is a bus that runs down the coastline (I stopped at the end at Amalfi).

Spend a day on Capri.

Positano really is very small so you can probably cover it in your 1/2 day. Use your two full days to go to Pompeii, take a bus or ferry around the other locations on the coast and/or, as suggested, go to Capri.

Paestum is worth a day, and you can get there from Positano by bus or ferry and bus.

Are you using Positano as a base to reach other places? It's not an ideal base (too small, not enough to do)...it's much easier to get there and spend time there from somewhere else (like a bigger city such as Sorrento).

How many nights?

I love the smaller places along the coast: Furore, Praiano, Minori, Atrani, Vietri sul Mare.

It depends on how energetic you're feeling. If you're in Positano for some R&R, you could spend a morning wandering around Positano, take the ferry to Amalfi town for the afternoon, and go to Capri the following day. If you're comfortable traveling by bus, there are other, smaller towns along the coast that are quite charming, as others have mentioned. Pompeii and Paestum are worthy destinations, but travel logistics from Positano to both those places can be challenging.

I loved the public bus ride down the coast to Amalfi. I wandered thru the town and the beautiful church. The front steps up to the church are amazing and I was lucky enough to see a wedding ending and the bride and groom descending the stairs (with her veil blowing in the wind behind her) a lovely photo. I had lunch in a small cafe. You can also go to a small town up the hill from Amalfi - Ravello.
The coast is beautiful from the bus, be sure to sit on the "water side" of the bus.