Hello, I have an iMac 21.5 inch 2017 model, with 2.3 Ghz Dual-Core Intel Core i5 specs. Recently I upgraded 250 GB SSD on my iMac, can I upgrade 500GB SSD on my iMac?

Hi, I am implementing an iPhone/iPad and mac app that allows users to send each other messages using the bonjour protocol. Basically, a server publishes his service over bonjour and the clients connected to the same wifi can discover his service and connect to it to start sending messages, it works fine with client and service communication but if I want to achieve peer to peer communication between multiple devices then I don't know how can I get list of connected Devices in network and how multiple devices can communicate with each other like peer to peer connectivity without using server/host? So how can be this possible?