Openfire scalability (1M to 10M Users)

Hi

I’m working on a large scale mobile chat app similar to Whatsapp and I have following questions:

1- I’m just wondering if Openfire is capable of handeling 1 to 10M users or not?

2- On average how many users each node can handle and what secification is required (RAM, CPU, etc)?

3- With hazelcast clustring how many nodes can we have?

4- Should I use Openfire for large scale userbase or I should look ingo Tigase or Ejabberd?

Looking forward to hearing form experts here.

Cheers