Elastic Search Master Node

Hi,

We're implementing Elastic Search, while installation, what do we mean by this "Enter the mininum number of master nodes :"

When I use one node ES works and when I try with 3 nodes, It doesn't ping.

Does no. of does depends on usage and amount of memory we have?

And can we use same instance of ES for two different PT versions i.e PT8.55 and PT8.56,

for example : CRM9.2 PT8.55 and I-Hub9.1 PT8.56 in one instance.

Thanks