Can HomeKit discover automatically new devices like does Alexa --- and HomeKit questions

I have more than 50 Alexa devices connected because HomeKit devices are TOO EXPENSIVE, especially on a large installation.

I want to find what device is HomeKit compatible

Can HomeKit discover automatically new devices like does Alexa ?

If my Internet is down are my devices still operational ?

Can HomeKit works with Alexa ?

I have a Mac mini Server can I use it as a HomeKit server ?

I have seen in the press that Apple is working with Amazon on a join venture for Home product

Will all Alexa product work with HomeKit ?

Thanks in advance for your answers

Cyril

P.S. add a topic for HomeKit ;)