How to develop a crypto exchange leveraging on third party API like coinbase, blockchain.com
I think you are somewhat confused on what you want to build. You can either (try to) build an exchange that sources Bitcoin from an exchange like Coinbase or Blockchain and then sells them on for a markup. Or you can build a P2P exchange like Bisq, Paxful, LocalBitcoins etc. If you do the former it isn't P2P and it is subject to limits enforced by the API provider. If you do the latter you have no use for an API from Coinbase or Blockchain. Bisq is open source so you could look at their code if you want to understand how their P2P exchange works.