I know that dedicated master nodes allow for better cluster operations as you get larger node counts and I am currently growing my cluster. I have some fairly low power boxes in storage that I think would make good master nodes (120GB SSD, 16GB RAM 4 cores @ 2Ghz) , I plan to roll out 2 of these and then as they only have a single power supply put a 3rd as a virtual machine on a host with full redundency with the power phases split such that the failure of a single phase could only take out one node.
Where I've run Masters on the data nodes till now I've set the discovery.zen.minimum_master_nodes based on the total number of nodes, I take it with dedicated master nodes I only set it with respect to those dedicated masters, however is there anything else I need to set with regards to the data nodes or will that just be made up of what ever data nodes are then able to start communication with what ever master quorum forms